[PATCH v2 00/17] Wire up getrandom() vDSO implementation on powerpc

[PATCH v2 00/17] Wire up getrandom() vDSO implementation on powerpc

[Christophe Leroy]

This series wires up getrandom() vDSO implementation on powerpc.

Tested on PPC32.

Performance on powerpc 885 (using kernel selftest):
	~# ./vdso_test_getrandom bench-single
	   vdso: 2500000 times in 7.897495392 seconds
	   libc: 2500000 times in 56.091632232 seconds
	syscall: 2500000 times in 55.704851989 seconds

Performance on powerpc 8321 (using kernel selftest):
	~# ./vdso_test_getrandom bench-single
	   vdso: 2500000 times in 2.017183250 seconds
	   libc: 2500000 times in 13.088533630 seconds
	syscall: 2500000 times in 12.952458068 seconds

Only build tested on PPC64. There is a problem with vdso_test_getrandom
selftest, it doesn't find vDSO symbol __kernel_getrandom. There is the
same problem with vdso_test_gettimeofday so it is not related to
getrandom.

On strange things to be clarified, there is the format of the key passed
to __arch_chacha20_blocks_nostack(). In struct vgetrandom_state it is
declared as a table of u32, but in reality it seems it is a flat storage
that needs to be loaded in reversed byte order, so it should either be
defined as a table of bytes, or as a table of __le32 but not a table of
u32. But this has no impact and can be clarified later and fixed in a
follow-up patch.

Changes in v2:
- Define VM_DROPPABLE for powerpc/32
- Fixes generic vDSO getrandom headers to enable CONFIG_COMPAT build.
- Fixed size of generation counter
- Fixed selftests to work on non x86 architectures

Christophe Leroy (17):
  asm-generic/unaligned.h: Extract common header for vDSO
  vdso: Clean header inclusion in getrandom
  vdso: Add __arch_get_k_vdso_rng_data()
  vdso: Add missing c-getrandom-y in Makefile
  vdso: Avoid call to memset() by getrandom
  vdso: Change getrandom's generation to unsigned long
  mm: Define VM_DROPPABLE for powerpc/32
  powerpc: Add little endian variants of LWZX_BE and STWX_BE
  powerpc/vdso32: Add crtsavres
  powerpc/vdso: Refactor CFLAGS for CVDSO build
  powerpc/vdso: Wire up getrandom() vDSO implementation
  selftests: vdso: Fix powerpc64 vdso_config
  selftests: vdso: Don't hard-code location of vDSO sources
  selftests: vdso: Make test_vdso_getrandom look for the right vDSO
    function
  selftests: vdso: Fix build of test_vdso_chacha
  selftests: vdso: Make VDSO function call more generic
  selftests: vdso: Add support for vdso_test_random for powerpc

 arch/powerpc/Kconfig                          |   1 +
 arch/powerpc/include/asm/asm-compat.h         |   8 +
 arch/powerpc/include/asm/mman.h               |   2 +-
 arch/powerpc/include/asm/vdso/getrandom.h     |  67 ++++
 arch/powerpc/include/asm/vdso/vsyscall.h      |   6 +
 arch/powerpc/include/asm/vdso_datapage.h      |   2 +
 arch/powerpc/kernel/asm-offsets.c             |   1 +
 arch/powerpc/kernel/vdso/Makefile             |  45 ++-
 arch/powerpc/kernel/vdso/getrandom.S          |  58 ++++
 arch/powerpc/kernel/vdso/gettimeofday.S       |  13 -
 arch/powerpc/kernel/vdso/vdso32.lds.S         |   1 +
 arch/powerpc/kernel/vdso/vdso64.lds.S         |   1 +
 arch/powerpc/kernel/vdso/vgetrandom-chacha.S  | 297 ++++++++++++++++++
 arch/powerpc/kernel/vdso/vgetrandom.c         |  14 +
 arch/x86/entry/vdso/vma.c                     |   3 +
 arch/x86/include/asm/pvclock.h                |   1 +
 arch/x86/include/asm/vdso/vsyscall.h          |  10 +-
 drivers/char/random.c                         |   5 +-
 fs/proc/task_mmu.c                            |   4 +-
 include/asm-generic/unaligned.h               |  11 +-
 include/linux/mm.h                            |   4 +-
 include/trace/events/mmflags.h                |   4 +-
 include/vdso/datapage.h                       |   2 +-
 include/vdso/getrandom.h                      |   2 +-
 include/vdso/helpers.h                        |   1 +
 include/vdso/unaligned.h                      |  15 +
 lib/vdso/Makefile                             |   1 +
 lib/vdso/getrandom.c                          |  30 +-
 tools/arch/powerpc/vdso                       |   1 +
 tools/arch/x86/vdso                           |   1 +
 tools/include/linux/linkage.h                 |   4 +
 tools/testing/selftests/vDSO/Makefile         |  12 +-
 tools/testing/selftests/vDSO/vdso_call.h      |  52 +++
 tools/testing/selftests/vDSO/vdso_config.h    |  14 +-
 .../selftests/vDSO/vdso_test_getrandom.c      |  11 +-
 35 files changed, 628 insertions(+), 76 deletions(-)
 create mode 100644 arch/powerpc/include/asm/vdso/getrandom.h
 create mode 100644 arch/powerpc/kernel/vdso/getrandom.S
 create mode 100644 arch/powerpc/kernel/vdso/vgetrandom-chacha.S
 create mode 100644 arch/powerpc/kernel/vdso/vgetrandom.c
 create mode 100644 include/vdso/unaligned.h
 create mode 120000 tools/arch/powerpc/vdso
 create mode 120000 tools/arch/x86/vdso
 create mode 100644 tools/testing/selftests/vDSO/vdso_call.h

-- 
2.44.0

[PATCH v2 01/17] asm-generic/unaligned.h: Extract common header for vDSO

[Christophe Leroy]

getrandom vDSO implementation requires __put_unaligned_t() and
__put_unaligned_t() but including asm-generic/unaligned.h pulls
too many other headers.

Follow the same approach as for most things in include/vdso/,
see for instance commit 8165b57bca21 ("linux/const.h: Extract
common header for vDSO"): Move __get_unaligned_t and __put_unaligned_t
into a new unaligned.h living in the vdso/ include directory.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 include/asm-generic/unaligned.h | 11 +----------
 include/vdso/unaligned.h        | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 10 deletions(-)
 create mode 100644 include/vdso/unaligned.h

diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h
index a84c64e5f11e..95acdd70b3b2 100644
--- a/include/asm-generic/unaligned.h
+++ b/include/asm-generic/unaligned.h
@@ -8,16 +8,7 @@
  */
 #include <linux/unaligned/packed_struct.h>
 #include <asm/byteorder.h>
-
-#define __get_unaligned_t(type, ptr) ({						\
-	const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);	\
-	__pptr->x;								\
-})
-
-#define __put_unaligned_t(type, val, ptr) do {					\
-	struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);		\
-	__pptr->x = (val);							\
-} while (0)
+#include <vdso/unaligned.h>
 
 #define get_unaligned(ptr)	__get_unaligned_t(typeof(*(ptr)), (ptr))
 #define put_unaligned(val, ptr) __put_unaligned_t(typeof(*(ptr)), (val), (ptr))
diff --git a/include/vdso/unaligned.h b/include/vdso/unaligned.h
new file mode 100644
index 000000000000..eee3d2a4dbe4
--- /dev/null
+++ b/include/vdso/unaligned.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_UNALIGNED_H
+#define __VDSO_UNALIGNED_H
+
+#define __get_unaligned_t(type, ptr) ({						\
+	const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);	\
+	__pptr->x;								\
+})
+
+#define __put_unaligned_t(type, val, ptr) do {					\
+	struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);		\
+	__pptr->x = (val);							\
+} while (0)
+
+#endif /* __VDSO_UNALIGNED_H */
-- 
2.44.0

[PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Christophe Leroy]

Building a VDSO32 on a 64 bits kernel is problematic when some
system headers are included. See commit 8c59ab839f52 ("lib/vdso:
Enable common headers") for more details.

Minimise the amount of headers by moving needed items into
dedicated common headers.

For PAGE_SIZE and PAGE_MASK, redefine them from CONFIG_PAGE_SHIFT
in the same way as commit cffaefd15a8f ("vdso: Use CONFIG_PAGE_SHIFT
in vdso/datapage.h")

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/x86/include/asm/pvclock.h |  1 +
 include/vdso/helpers.h         |  1 +
 lib/vdso/getrandom.c           | 15 ++++++++-------
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 0c92db84469d..6e4f8fae3ce9 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -5,6 +5,7 @@
 #include <asm/clocksource.h>
 #include <asm/pvclock-abi.h>
 
+struct timespec64;
 /* some helper functions for xen and kvm pv clock sources */
 u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
 u64 pvclock_clocksource_read_nowd(struct pvclock_vcpu_time_info *src);
diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
index 73501149439d..3ddb03bb05cb 100644
--- a/include/vdso/helpers.h
+++ b/include/vdso/helpers.h
@@ -4,6 +4,7 @@
 
 #ifndef __ASSEMBLY__
 
+#include <asm/barrier.h>
 #include <vdso/datapage.h>
 
 static __always_inline u32 vdso_read_begin(const struct vdso_data *vd)
diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index b230f0b10832..cab153c5f9be 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -3,15 +3,13 @@
  * Copyright (C) 2022-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  */
 
-#include <linux/cache.h>
-#include <linux/kernel.h>
-#include <linux/time64.h>
+#include <linux/minmax.h>
 #include <vdso/datapage.h>
 #include <vdso/getrandom.h>
+#include <vdso/unaligned.h>
 #include <asm/vdso/getrandom.h>
-#include <asm/vdso/vsyscall.h>
-#include <asm/unaligned.h>
 #include <uapi/linux/mman.h>
+#include <uapi/linux/random.h>
 
 #define MEMCPY_AND_ZERO_SRC(type, dst, src, len) do {				\
 	while (len >= sizeof(type)) {						\
@@ -23,6 +21,9 @@
 	}									\
 } while (0)
 
+#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
+#define _PAGE_MASK (~(_PAGE_SIZE - 1))
+
 static void memcpy_and_zero_src(void *dst, void *src, size_t len)
 {
 	if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
@@ -64,7 +65,7 @@ static __always_inline ssize_t
 __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_t len,
 		       unsigned int flags, void *opaque_state, size_t opaque_len)
 {
-	ssize_t ret = min_t(size_t, INT_MAX & PAGE_MASK /* = MAX_RW_COUNT */, len);
+	ssize_t ret = min_t(size_t, INT_MAX & _PAGE_MASK /* = MAX_RW_COUNT */, len);
 	struct vgetrandom_state *state = opaque_state;
 	size_t batch_len, nblocks, orig_len = len;
 	bool in_use, have_retried = false;
@@ -82,7 +83,7 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
 	}
 
 	/* The state must not straddle a page, since pages can be zeroed at any time. */
-	if (unlikely(((unsigned long)opaque_state & ~PAGE_MASK) + sizeof(*state) > PAGE_SIZE))
+	if (unlikely(((unsigned long)opaque_state & ~_PAGE_MASK) + sizeof(*state) > _PAGE_SIZE))
 		return -EFAULT;
 
 	/* If the caller passes the wrong size, which might happen due to CRIU, fallback. */
-- 
2.44.0

[PATCH v2 03/17] vdso: Add __arch_get_k_vdso_rng_data()

[Christophe Leroy]

_vdso_data is specific to x86 and __arch_get_k_vdso_data() is provided
so that all architectures can provide the requested pointer.

Do the same with _vdso_rng_data, provide __arch_get_k_vdso_rng_data()
and don't use x86 _vdso_rng_data directly.

Until now vdso/vsyscall.h was only included by time/vsyscall.c but now
it will also be included in char/random.c, leading to a duplicate
declaration of _vdso_data and _vdso_rng_data.

To fix this issue, move declaration in a C file. vma.c looks like the
most appropriate candidate. Don't need to replace the definitions in
vsyscall.h by declarations as declarations are already in asm/vvar.h

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v2: Move x86 DEFINE_VVAR(_vdso_data) and DEFINE_VVAR(_vdso_rng_data) in vma.c
---
 arch/x86/entry/vdso/vma.c            |  3 +++
 arch/x86/include/asm/vdso/vsyscall.h | 10 +++++++---
 drivers/char/random.c                |  5 +++--
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 6d83ceb7f1ba..b8fed8b8b9cc 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -38,6 +38,9 @@ struct vdso_data *arch_get_vdso_data(void *vvar_page)
 }
 #undef EMIT_VVAR
 
+DEFINE_VVAR(struct vdso_data, _vdso_data);
+DEFINE_VVAR_SINGLE(struct vdso_rng_data, _vdso_rng_data);
+
 unsigned int vclocks_used __read_mostly;
 
 #if defined(CONFIG_X86_64)
diff --git a/arch/x86/include/asm/vdso/vsyscall.h b/arch/x86/include/asm/vdso/vsyscall.h
index 972415a8be31..67fedf1698b5 100644
--- a/arch/x86/include/asm/vdso/vsyscall.h
+++ b/arch/x86/include/asm/vdso/vsyscall.h
@@ -9,9 +9,6 @@
 #include <asm/vgtod.h>
 #include <asm/vvar.h>
 
-DEFINE_VVAR(struct vdso_data, _vdso_data);
-DEFINE_VVAR_SINGLE(struct vdso_rng_data, _vdso_rng_data);
-
 /*
  * Update the vDSO data page to keep in sync with kernel timekeeping.
  */
@@ -22,6 +19,13 @@ struct vdso_data *__x86_get_k_vdso_data(void)
 }
 #define __arch_get_k_vdso_data __x86_get_k_vdso_data
 
+static __always_inline
+struct vdso_rng_data *__x86_get_k_vdso_rng_data(void)
+{
+	return &_vdso_rng_data;
+}
+#define __arch_get_k_vdso_rng_data __x86_get_k_vdso_rng_data
+
 /* The asm-generic header needs to be included after the definitions above */
 #include <asm-generic/vdso/vsyscall.h>
 
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 87fe61295ea1..77968309e2c2 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -59,6 +59,7 @@
 #ifdef CONFIG_VDSO_GETRANDOM
 #include <vdso/getrandom.h>
 #include <vdso/datapage.h>
+#include <vdso/vsyscall.h>
 #endif
 #include <asm/archrandom.h>
 #include <asm/processor.h>
@@ -282,7 +283,7 @@ static void crng_reseed(struct work_struct *work)
 	 * is ordered with the write above to base_crng.generation. Pairs with
 	 * the smp_rmb() before the syscall in the vDSO code.
 	 */
-	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
+	smp_store_release(&__arch_get_k_vdso_rng_data()->generation, next_gen + 1);
 #endif
 	if (!static_branch_likely(&crng_is_ready))
 		crng_init = CRNG_READY;
@@ -735,7 +736,7 @@ static void __cold _credit_init_bits(size_t bits)
 			queue_work(system_unbound_wq, &set_ready);
 		atomic_notifier_call_chain(&random_ready_notifier, 0, NULL);
 #ifdef CONFIG_VDSO_GETRANDOM
-		WRITE_ONCE(_vdso_rng_data.is_ready, true);
+		WRITE_ONCE(__arch_get_k_vdso_rng_data()->is_ready, true);
 #endif
 		wake_up_interruptible(&crng_init_wait);
 		kill_fasync(&fasync, SIGIO, POLL_IN);
-- 
2.44.0

[PATCH v2 04/17] vdso: Add missing c-getrandom-y in Makefile

[Christophe Leroy]

Same as for gettimeofday CVDSO implementation, add c-getrandom-y
to ease the inclusion of lib/vdso/getrandom.c in architectures
VDSO builds.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 lib/vdso/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/vdso/Makefile b/lib/vdso/Makefile
index 9f031eafc465..cedbf15f8087 100644
--- a/lib/vdso/Makefile
+++ b/lib/vdso/Makefile
@@ -4,6 +4,7 @@ GENERIC_VDSO_MK_PATH := $(abspath $(lastword $(MAKEFILE_LIST)))
 GENERIC_VDSO_DIR := $(dir $(GENERIC_VDSO_MK_PATH))
 
 c-gettimeofday-$(CONFIG_GENERIC_GETTIMEOFDAY) := $(addprefix $(GENERIC_VDSO_DIR), gettimeofday.c)
+c-getrandom-$(CONFIG_VDSO_GETRANDOM) := $(addprefix $(GENERIC_VDSO_DIR), getrandom.c)
 
 # This cmd checks that the vdso library does not contain dynamic relocations.
 # It has to be called after the linking of the vdso library and requires it
-- 
2.44.0

[PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Christophe Leroy]

With the current implementation, __cvdso_getrandom_data() calls
memset(), which is unexpected in the VDSO.

Rewrite opaque data initialisation to avoid memset().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 lib/vdso/getrandom.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index cab153c5f9be..4a56f45141b4 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/minmax.h>
+#include <linux/array_size.h>
 #include <vdso/datapage.h>
 #include <vdso/getrandom.h>
 #include <vdso/unaligned.h>
@@ -74,11 +75,15 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
 	u32 counter[2] = { 0 };
 
 	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags)) {
-		*(struct vgetrandom_opaque_params *)opaque_state = (struct vgetrandom_opaque_params) {
-			.size_of_opaque_state = sizeof(*state),
-			.mmap_prot = PROT_READ | PROT_WRITE,
-			.mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS
-		};
+		struct vgetrandom_opaque_params *params = opaque_state;
+		int i;
+
+		params->size_of_opaque_state = sizeof(*state);
+		params->mmap_prot = PROT_READ | PROT_WRITE;
+		params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
+		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
+			params->reserved[i] = 0;
+
 		return 0;
 	}
 
-- 
2.44.0

[PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[Christophe Leroy]

Performing SMP atomic operations on u64 fails on powerpc32.

Random driver generation is handled as unsigned long not u64,
see for instance base_cnrg or struct crng.

Use the same type for vDSO's getrandom as it gets copied
from the above. This is also in line with the local
current_generation which is already an unsigned long.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 include/vdso/datapage.h  | 2 +-
 include/vdso/getrandom.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index b85f24cac3f5..00b66a9b5778 100644
--- a/include/vdso/datapage.h
+++ b/include/vdso/datapage.h
@@ -123,7 +123,7 @@ struct vdso_data {
  * @is_ready:	boolean signaling whether the RNG is initialized
  */
 struct vdso_rng_data {
-	u64	generation;
+	unsigned long	generation;
 	u8	is_ready;
 };
 
diff --git a/include/vdso/getrandom.h b/include/vdso/getrandom.h
index a8b7c14b0ae0..36fd166bf330 100644
--- a/include/vdso/getrandom.h
+++ b/include/vdso/getrandom.h
@@ -38,7 +38,7 @@ struct vgetrandom_state {
 		};
 		u8		batch_key[CHACHA_BLOCK_SIZE * 2];
 	};
-	u64			generation;
+	unsigned long		generation;
 	u8			pos;
 	bool 			in_use;
 };
-- 
2.44.0

[PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32

[Christophe Leroy]

Commit 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always
lazily freeable mappings") only adds VM_DROPPABLE for 64 bits
architectures.

In order to also use the getrandom vDSO implementation on powerpc/32,
use VM_ARCH_1 for VM_DROPPABLE on powerpc/32. This is possible because
VM_ARCH_1 is used for VM_SAO on powerpc and VM_SAO is only for
powerpc/64.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 fs/proc/task_mmu.c             | 4 +++-
 include/linux/mm.h             | 4 +++-
 include/trace/events/mmflags.h | 4 ++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5f171ad7b436..4a3fe961cbf6 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -987,8 +987,10 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 #ifdef CONFIG_X86_USER_SHADOW_STACK
 		[ilog2(VM_SHADOW_STACK)] = "ss",
 #endif
-#ifdef CONFIG_64BIT
+#if VM_DROPPABLE != VM_NONE
 		[ilog2(VM_DROPPABLE)] = "dp",
+#endif
+#ifdef CONFIG_64BIT
 		[ilog2(VM_SEALED)] = "sl",
 #endif
 	};
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c4b238a20b76..865d3e21ee5e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -359,7 +359,7 @@ extern unsigned int kobjsize(const void *objp);
 
 #if defined(CONFIG_X86)
 # define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
-#elif defined(CONFIG_PPC)
+#elif defined(CONFIG_PPC64)
 # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
 #elif defined(CONFIG_PARISC)
 # define VM_GROWSUP	VM_ARCH_1
@@ -409,6 +409,8 @@ extern unsigned int kobjsize(const void *objp);
 #ifdef CONFIG_64BIT
 #define VM_DROPPABLE_BIT	40
 #define VM_DROPPABLE		BIT(VM_DROPPABLE_BIT)
+#elif defined(CONFIG_PPC32)
+#define VM_DROPPABLE		VM_ARCH_1
 #else
 #define VM_DROPPABLE		VM_NONE
 #endif
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index b63d211bd141..9820cbfbcb14 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -143,7 +143,7 @@ IF_HAVE_PG_ARCH_X(arch_3)
 
 #if defined(CONFIG_X86)
 #define __VM_ARCH_SPECIFIC_1 {VM_PAT,     "pat"           }
-#elif defined(CONFIG_PPC)
+#elif defined(CONFIG_PPC64)
 #define __VM_ARCH_SPECIFIC_1 {VM_SAO,     "sao"           }
 #elif defined(CONFIG_PARISC)
 #define __VM_ARCH_SPECIFIC_1 {VM_GROWSUP,	"growsup"	}
@@ -165,7 +165,7 @@ IF_HAVE_PG_ARCH_X(arch_3)
 # define IF_HAVE_UFFD_MINOR(flag, name)
 #endif
 
-#ifdef CONFIG_64BIT
+#if VM_DROPPABLE != VM_NONE
 # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
 #else
 # define IF_HAVE_VM_DROPPABLE(flag, name)
-- 
2.44.0

[PATCH v2 08/17] powerpc: Add little endian variants of LWZX_BE and STWX_BE

[Christophe Leroy]

To support getrandom in VDSO which is based on little endian storage,
add macros equivalent to LWZX_BE and STWX_BE for little endian
accesses.

Put them outside of __powerpc64__ #ifdef so that they can also be used
for PPC32.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/include/asm/asm-compat.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h
index 2bc53c646ccd..6e53a80917ef 100644
--- a/arch/powerpc/include/asm/asm-compat.h
+++ b/arch/powerpc/include/asm/asm-compat.h
@@ -61,4 +61,12 @@
 
 #endif
 
+#ifdef __BIG_ENDIAN__
+#define LWZX_LE	stringify_in_c(lwbrx)
+#define STWX_LE	stringify_in_c(stwbrx)
+#else
+#define LWZX_LE	stringify_in_c(lwzx)
+#define STWX_LE	stringify_in_c(stwx)
+#endif
+
 #endif /* _ASM_POWERPC_ASM_COMPAT_H */
-- 
2.44.0

[PATCH v2 09/17] powerpc/vdso32: Add crtsavres

[Christophe Leroy]

Commit 08c18b63d965 ("powerpc/vdso32: Add missing _restgpr_31_x to fix
build failure") added _restgpr_31_x to the vdso for gettimeofday, but
the work on getrandom shows that we will need more of those functions.

Remove _restgpr_31_x and link in crtsavres.o so that we get all
save/restore functions when optimising the kernel for size.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/kernel/vdso/Makefile       |  5 ++++-
 arch/powerpc/kernel/vdso/gettimeofday.S | 13 -------------
 2 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
index 1425b6edc66b..c07a425b8f78 100644
--- a/arch/powerpc/kernel/vdso/Makefile
+++ b/arch/powerpc/kernel/vdso/Makefile
@@ -43,6 +43,7 @@ else
 endif
 
 targets := $(obj-vdso32) vdso32.so.dbg vgettimeofday-32.o
+targets += crtsavres-32.o
 obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
 targets += $(obj-vdso64) vdso64.so.dbg vgettimeofday-64.o
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
@@ -68,7 +69,7 @@ targets += vdso64.lds
 CPPFLAGS_vdso64.lds += -P -C
 
 # link rule for the .so file, .lds has to be first
-$(obj)/vdso32.so.dbg: $(obj)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday-32.o FORCE
+$(obj)/vdso32.so.dbg: $(obj)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday-32.o $(obj)/crtsavres-32.o FORCE
 	$(call if_changed,vdso32ld_and_check)
 $(obj)/vdso64.so.dbg: $(obj)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday-64.o FORCE
 	$(call if_changed,vdso64ld_and_check)
@@ -76,6 +77,8 @@ $(obj)/vdso64.so.dbg: $(obj)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday-64.o
 # assembly rules for the .S files
 $(obj-vdso32): %-32.o: %.S FORCE
 	$(call if_changed_dep,vdso32as)
+$(obj)/crtsavres-32.o: %-32.o: $(srctree)/arch/powerpc/lib/crtsavres.S FORCE
+	$(call if_changed_dep,vdso32as)
 $(obj)/vgettimeofday-32.o: %-32.o: %.c FORCE
 	$(call if_changed_dep,vdso32cc)
 $(obj-vdso64): %-64.o: %.S FORCE
diff --git a/arch/powerpc/kernel/vdso/gettimeofday.S b/arch/powerpc/kernel/vdso/gettimeofday.S
index 48fc6658053a..67254ac9c8bb 100644
--- a/arch/powerpc/kernel/vdso/gettimeofday.S
+++ b/arch/powerpc/kernel/vdso/gettimeofday.S
@@ -118,16 +118,3 @@ V_FUNCTION_END(__kernel_clock_getres)
 V_FUNCTION_BEGIN(__kernel_time)
 	cvdso_call __c_kernel_time call_time=1
 V_FUNCTION_END(__kernel_time)
-
-/* Routines for restoring integer registers, called by the compiler.  */
-/* Called with r11 pointing to the stack header word of the caller of the */
-/* function, just beyond the end of the integer restore area.  */
-#ifndef __powerpc64__
-_GLOBAL(_restgpr_31_x)
-_GLOBAL(_rest32gpr_31_x)
-	lwz	r0,4(r11)
-	lwz	r31,-4(r11)
-	mtlr	r0
-	mr	r1,r11
-	blr
-#endif
-- 
2.44.0

[PATCH v2 10/17] powerpc/vdso: Refactor CFLAGS for CVDSO build

[Christophe Leroy]

In order to avoid duplication when we add new VDSO functionnalities
in C like getrandom, refactor common CFLAGS.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/kernel/vdso/Makefile | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
index c07a425b8f78..cd4ed09864f0 100644
--- a/arch/powerpc/kernel/vdso/Makefile
+++ b/arch/powerpc/kernel/vdso/Makefile
@@ -10,11 +10,6 @@ obj-vdso64 = sigtramp64-64.o gettimeofday-64.o datapage-64.o cacheflush-64.o not
 
 ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday-32.o += -include $(c-gettimeofday-y)
-  CFLAGS_vgettimeofday-32.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
-  CFLAGS_vgettimeofday-32.o += $(call cc-option, -fno-stack-protector)
-  CFLAGS_vgettimeofday-32.o += -DDISABLE_BRANCH_PROFILING
-  CFLAGS_vgettimeofday-32.o += -ffreestanding -fasynchronous-unwind-tables
-  CFLAGS_REMOVE_vgettimeofday-32.o = $(CC_FLAGS_FTRACE)
   CFLAGS_REMOVE_vgettimeofday-32.o += -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc
   # This flag is supported by clang for 64-bit but not 32-bit so it will cause
   # an unused command line flag warning for this file.
@@ -22,11 +17,6 @@ ifneq ($(c-gettimeofday-y),)
   CFLAGS_REMOVE_vgettimeofday-32.o += -fno-stack-clash-protection
   endif
   CFLAGS_vgettimeofday-64.o += -include $(c-gettimeofday-y)
-  CFLAGS_vgettimeofday-64.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
-  CFLAGS_vgettimeofday-64.o += $(call cc-option, -fno-stack-protector)
-  CFLAGS_vgettimeofday-64.o += -DDISABLE_BRANCH_PROFILING
-  CFLAGS_vgettimeofday-64.o += -ffreestanding -fasynchronous-unwind-tables
-  CFLAGS_REMOVE_vgettimeofday-64.o = $(CC_FLAGS_FTRACE)
 # Go prior to 1.16.x assumes r30 is not clobbered by any VDSO code. That used to be true
 # by accident when the VDSO was hand-written asm code, but may not be now that the VDSO is
 # compiler generated. To avoid breaking Go tell GCC not to use r30. Impact on code
@@ -49,7 +39,12 @@ targets += $(obj-vdso64) vdso64.so.dbg vgettimeofday-64.o
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
 
 ccflags-y := -fno-common -fno-builtin
+ccflags-y += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+ccflags-y += $(call cc-option, -fno-stack-protector)
+ccflags-y += -DDISABLE_BRANCH_PROFILING
+ccflags-y += -ffreestanding -fasynchronous-unwind-tables
 ldflags-y := -Wl,--hash-style=both -nostdlib -shared -z noexecstack $(CLANG_FLAGS)
+ccflags-remove-y := $(CC_FLAGS_FTRACE)
 ldflags-$(CONFIG_LD_IS_LLD) += $(call cc-option,--ld-path=$(LD),-fuse-ld=lld)
 ldflags-$(CONFIG_LD_ORPHAN_WARN) += -Wl,--orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
 
-- 
2.44.0

[PATCH v2 11/17] powerpc/vdso: Wire up getrandom() vDSO implementation

[Christophe Leroy]

To be consistent with other VDSO functions, the function is called
__kernel_getrandom()

__arch_chacha20_blocks_nostack() fonction is implemented basically
with 32 bits operations. It performs 4 QUARTERROUND operations in
parallele. There are enough registers to avoid using the stack:

On input:
	r3: output bytes
	r4: 32-byte key input
	r5: 8-byte counter input/output
	r6: number of 64-byte blocks to write to output

During operation:
	r0: counter of blocks (initialised with r6)
	r4: Value '4' after key has been read, used for indexing
	r6-r13: key
	r14-r15: block counter
	r16-r31: chacha state

At the end:
	r0, r6-r13: Zeroised
	r14-r31: Restored

Performance on powerpc 885 (using kernel selftest):
	~# ./vdso_test_getrandom bench-single
	   vdso: 2500000 times in 7.897495392 seconds
	   libc: 2500000 times in 56.091632232 seconds
	syscall: 2500000 times in 55.704851989 seconds

Performance on powerpc 8321 (using kernel selftest):
	~# ./vdso_test_getrandom bench-single
	   vdso: 2500000 times in 2.017183250 seconds
	   libc: 2500000 times in 13.088533630 seconds
	syscall: 2500000 times in 12.952458068 seconds

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/Kconfig                         |   1 +
 arch/powerpc/include/asm/mman.h              |   2 +-
 arch/powerpc/include/asm/vdso/getrandom.h    |  67 +++++
 arch/powerpc/include/asm/vdso/vsyscall.h     |   6 +
 arch/powerpc/include/asm/vdso_datapage.h     |   2 +
 arch/powerpc/kernel/asm-offsets.c            |   1 +
 arch/powerpc/kernel/vdso/Makefile            |  27 +-
 arch/powerpc/kernel/vdso/getrandom.S         |  58 ++++
 arch/powerpc/kernel/vdso/vdso32.lds.S        |   1 +
 arch/powerpc/kernel/vdso/vdso64.lds.S        |   1 +
 arch/powerpc/kernel/vdso/vgetrandom-chacha.S | 297 +++++++++++++++++++
 arch/powerpc/kernel/vdso/vgetrandom.c        |  14 +
 12 files changed, 471 insertions(+), 6 deletions(-)
 create mode 100644 arch/powerpc/include/asm/vdso/getrandom.h
 create mode 100644 arch/powerpc/kernel/vdso/getrandom.S
 create mode 100644 arch/powerpc/kernel/vdso/vgetrandom-chacha.S
 create mode 100644 arch/powerpc/kernel/vdso/vgetrandom.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index d7b09b064a8a..b45452ac4a73 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -311,6 +311,7 @@ config PPC
 	select SYSCTL_EXCEPTION_TRACE
 	select THREAD_INFO_IN_TASK
 	select TRACE_IRQFLAGS_SUPPORT
+	select VDSO_GETRANDOM
 	#
 	# Please keep this list sorted alphabetically.
 	#
diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
index 17a77d47ed6d..42a51a993d94 100644
--- a/arch/powerpc/include/asm/mman.h
+++ b/arch/powerpc/include/asm/mman.h
@@ -6,7 +6,7 @@
 
 #include <uapi/asm/mman.h>
 
-#ifdef CONFIG_PPC64
+#if defined(CONFIG_PPC64) && !defined(BUILD_VDSO)
 
 #include <asm/cputable.h>
 #include <linux/mm.h>
diff --git a/arch/powerpc/include/asm/vdso/getrandom.h b/arch/powerpc/include/asm/vdso/getrandom.h
new file mode 100644
index 000000000000..b37e581b02cb
--- /dev/null
+++ b/arch/powerpc/include/asm/vdso/getrandom.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
+ */
+#ifndef _ASM_POWERPC_VDSO_GETRANDOM_H
+#define _ASM_POWERPC_VDSO_GETRANDOM_H
+
+#ifndef __ASSEMBLY__
+
+static __always_inline int do_syscall_3(const unsigned long _r0, const unsigned long _r3,
+					const unsigned long _r4, const unsigned long _r5)
+{
+	register long r0 asm("r0") = _r0;
+	register unsigned long r3 asm("r3") = _r3;
+	register unsigned long r4 asm("r4") = _r4;
+	register unsigned long r5 asm("r5") = _r5;
+	register int ret asm ("r3");
+
+	asm volatile(
+		"       sc\n"
+		"	bns+	1f\n"
+		"	neg	%0, %0\n"
+		"1:\n"
+	: "=r" (ret), "+r" (r4), "+r" (r5), "+r" (r0)
+	: "r" (r3)
+	: "memory", "r6", "r7", "r8", "r9", "r10", "r11", "r12", "cr0", "ctr");
+
+	return ret;
+}
+
+/**
+ * getrandom_syscall - Invoke the getrandom() syscall.
+ * @buffer:	Destination buffer to fill with random bytes.
+ * @len:	Size of @buffer in bytes.
+ * @flags:	Zero or more GRND_* flags.
+ * Returns:	The number of bytes written to @buffer, or a negative value indicating an error.
+ */
+static __always_inline ssize_t getrandom_syscall(void *buffer, size_t len, unsigned int flags)
+{
+	return do_syscall_3(__NR_getrandom, (unsigned long)buffer,
+			    (unsigned long)len, (unsigned long)flags);
+}
+
+static __always_inline struct vdso_rng_data *__arch_get_vdso_rng_data(void)
+{
+	BUILD_BUG();
+}
+
+ssize_t __c_kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state,
+			     size_t opaque_len, const struct vdso_rng_data *vd);
+
+/**
+ * __arch_chacha20_blocks_nostack - Generate ChaCha20 stream without using the stack.
+ * @dst_bytes:	Destination buffer to hold @nblocks * 64 bytes of output.
+ * @key:	32-byte input key.
+ * @counter:	8-byte counter, read on input and updated on return.
+ * @nblocks:	Number of blocks to generate.
+ *
+ * Generates a given positive number of blocks of ChaCha20 output with nonce=0, and does not write
+ * to any stack or memory outside of the parameters passed to it, in order to mitigate stack data
+ * leaking into forked child processes.
+ */
+void __arch_chacha20_blocks_nostack(u8 *dst_bytes, const u32 *key, u32 *counter, size_t nblocks);
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* _ASM_POWERPC_VDSO_GETRANDOM_H */
diff --git a/arch/powerpc/include/asm/vdso/vsyscall.h b/arch/powerpc/include/asm/vdso/vsyscall.h
index 48cf23f1e273..92f480d8cc6d 100644
--- a/arch/powerpc/include/asm/vdso/vsyscall.h
+++ b/arch/powerpc/include/asm/vdso/vsyscall.h
@@ -17,6 +17,12 @@ struct vdso_data *__arch_get_k_vdso_data(void)
 }
 #define __arch_get_k_vdso_data __arch_get_k_vdso_data
 
+static __always_inline
+struct vdso_rng_data *__arch_get_k_vdso_rng_data(void)
+{
+	return &vdso_data->rng_data;
+}
+
 /* The asm-generic header needs to be included after the definitions above */
 #include <asm-generic/vdso/vsyscall.h>
 
diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index a585c8e538ff..e17500c5237e 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -83,6 +83,7 @@ struct vdso_arch_data {
 	__u32 compat_syscall_map[SYSCALL_MAP_SIZE];	/* Map of compat syscalls */
 
 	struct vdso_data data[CS_BASES];
+	struct vdso_rng_data rng_data;
 };
 
 #else /* CONFIG_PPC64 */
@@ -95,6 +96,7 @@ struct vdso_arch_data {
 	__u32 syscall_map[SYSCALL_MAP_SIZE]; /* Map of syscalls */
 	__u32 compat_syscall_map[0];	/* No compat syscalls on PPC32 */
 	struct vdso_data data[CS_BASES];
+	struct vdso_rng_data rng_data;
 };
 
 #endif /* CONFIG_PPC64 */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 23733282de4d..eedb2e04c785 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -335,6 +335,7 @@ int main(void)
 
 	/* datapage offsets for use by vdso */
 	OFFSET(VDSO_DATA_OFFSET, vdso_arch_data, data);
+	OFFSET(VDSO_RNG_DATA_OFFSET, vdso_arch_data, rng_data);
 	OFFSET(CFG_TB_TICKS_PER_SEC, vdso_arch_data, tb_ticks_per_sec);
 #ifdef CONFIG_PPC64
 	OFFSET(CFG_ICACHE_BLOCKSZ, vdso_arch_data, icache_block_size);
diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
index cd4ed09864f0..9109677b2f39 100644
--- a/arch/powerpc/kernel/vdso/Makefile
+++ b/arch/powerpc/kernel/vdso/Makefile
@@ -8,6 +8,9 @@ include $(srctree)/lib/vdso/Makefile
 obj-vdso32 = sigtramp32-32.o gettimeofday-32.o datapage-32.o cacheflush-32.o note-32.o getcpu-32.o
 obj-vdso64 = sigtramp64-64.o gettimeofday-64.o datapage-64.o cacheflush-64.o note-64.o getcpu-64.o
 
+obj-vdso32 += getrandom-32.o vgetrandom-chacha-32.o
+obj-vdso64 += getrandom-64.o vgetrandom-chacha-64.o
+
 ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday-32.o += -include $(c-gettimeofday-y)
   CFLAGS_REMOVE_vgettimeofday-32.o += -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc
@@ -24,6 +27,16 @@ ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday-64.o += $(call cc-option, -ffixed-r30)
 endif
 
+ifneq ($(c-getrandom-y),)
+  CFLAGS_vgetrandom-32.o += -include $(c-getrandom-y)
+  CFLAGS_REMOVE_vgetrandom-32.o += -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc
+  ifdef CONFIG_CC_IS_CLANG
+  CFLAGS_REMOVE_vgetrandom-32.o += -fno-stack-clash-protection
+  endif
+  CFLAGS_vgetrandom-64.o += -include $(c-getrandom-y)
+  CFLAGS_vgetrandom-64.o += $(call cc-option, -ffixed-r30)
+endif
+
 # Build rules
 
 ifdef CROSS32_COMPILE
@@ -32,13 +45,13 @@ else
     VDSOCC := $(CC)
 endif
 
-targets := $(obj-vdso32) vdso32.so.dbg vgettimeofday-32.o
+targets := $(obj-vdso32) vdso32.so.dbg vgettimeofday-32.o vgetrandom-32.o
 targets += crtsavres-32.o
 obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
-targets += $(obj-vdso64) vdso64.so.dbg vgettimeofday-64.o
+targets += $(obj-vdso64) vdso64.so.dbg vgettimeofday-64.o vgetrandom-64.o
 obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
 
-ccflags-y := -fno-common -fno-builtin
+ccflags-y := -fno-common -fno-builtin -DBUILD_VDSO
 ccflags-y += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 ccflags-y += $(call cc-option, -fno-stack-protector)
 ccflags-y += -DDISABLE_BRANCH_PROFILING
@@ -64,9 +77,9 @@ targets += vdso64.lds
 CPPFLAGS_vdso64.lds += -P -C
 
 # link rule for the .so file, .lds has to be first
-$(obj)/vdso32.so.dbg: $(obj)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday-32.o $(obj)/crtsavres-32.o FORCE
+$(obj)/vdso32.so.dbg: $(obj)/vdso32.lds $(obj-vdso32) $(obj)/vgettimeofday-32.o $(obj)/vgetrandom-32.o $(obj)/crtsavres-32.o FORCE
 	$(call if_changed,vdso32ld_and_check)
-$(obj)/vdso64.so.dbg: $(obj)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday-64.o FORCE
+$(obj)/vdso64.so.dbg: $(obj)/vdso64.lds $(obj-vdso64) $(obj)/vgettimeofday-64.o $(obj)/vgetrandom-64.o FORCE
 	$(call if_changed,vdso64ld_and_check)
 
 # assembly rules for the .S files
@@ -76,10 +89,14 @@ $(obj)/crtsavres-32.o: %-32.o: $(srctree)/arch/powerpc/lib/crtsavres.S FORCE
 	$(call if_changed_dep,vdso32as)
 $(obj)/vgettimeofday-32.o: %-32.o: %.c FORCE
 	$(call if_changed_dep,vdso32cc)
+$(obj)/vgetrandom-32.o: %-32.o: %.c FORCE
+	$(call if_changed_dep,vdso32cc)
 $(obj-vdso64): %-64.o: %.S FORCE
 	$(call if_changed_dep,vdso64as)
 $(obj)/vgettimeofday-64.o: %-64.o: %.c FORCE
 	$(call if_changed_dep,cc_o_c)
+$(obj)/vgetrandom-64.o: %-64.o: %.c FORCE
+	$(call if_changed_dep,cc_o_c)
 
 # Generate VDSO offsets using helper script
 gen-vdso32sym := $(src)/gen_vdso32_offsets.sh
diff --git a/arch/powerpc/kernel/vdso/getrandom.S b/arch/powerpc/kernel/vdso/getrandom.S
new file mode 100644
index 000000000000..a957cd2b2b03
--- /dev/null
+++ b/arch/powerpc/kernel/vdso/getrandom.S
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Userland implementation of getrandom() for processes
+ * for use in the vDSO
+ *
+ * Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
+ */
+#include <asm/processor.h>
+#include <asm/ppc_asm.h>
+#include <asm/vdso.h>
+#include <asm/vdso_datapage.h>
+#include <asm/asm-offsets.h>
+#include <asm/unistd.h>
+
+/*
+ * The macro sets two stack frames, one for the caller and one for the callee
+ * because there are no requirement for the caller to set a stack frame when
+ * calling VDSO so it may have omitted to set one, especially on PPC64
+ */
+
+.macro cvdso_call funct
+  .cfi_startproc
+	PPC_STLU	r1, -PPC_MIN_STKFRM(r1)
+  .cfi_adjust_cfa_offset PPC_MIN_STKFRM
+	mflr		r0
+	PPC_STLU	r1, -PPC_MIN_STKFRM(r1)
+  .cfi_adjust_cfa_offset PPC_MIN_STKFRM
+	PPC_STL		r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
+  .cfi_rel_offset lr, PPC_MIN_STKFRM + PPC_LR_STKOFF
+#ifdef __powerpc64__
+	PPC_STL		r2, PPC_MIN_STKFRM + STK_GOT(r1)
+  .cfi_rel_offset r2, PPC_MIN_STKFRM + STK_GOT
+#endif
+	get_datapage	r8
+	addi		r8, r8, VDSO_RNG_DATA_OFFSET
+	bl		CFUNC(DOTSYM(\funct))
+	PPC_LL		r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
+#ifdef __powerpc64__
+	PPC_LL		r2, PPC_MIN_STKFRM + STK_GOT(r1)
+  .cfi_restore r2
+#endif
+	cmpwi		r3, 0
+	mtlr		r0
+	addi		r1, r1, 2 * PPC_MIN_STKFRM
+  .cfi_restore lr
+  .cfi_def_cfa_offset 0
+	crclr		so
+	bgelr+
+	crset		so
+	neg		r3, r3
+	blr
+  .cfi_endproc
+.endm
+
+	.text
+V_FUNCTION_BEGIN(__kernel_getrandom)
+	cvdso_call __c_kernel_getrandom
+V_FUNCTION_END(__kernel_getrandom)
diff --git a/arch/powerpc/kernel/vdso/vdso32.lds.S b/arch/powerpc/kernel/vdso/vdso32.lds.S
index 8f57107000a2..7b41d5d256e8 100644
--- a/arch/powerpc/kernel/vdso/vdso32.lds.S
+++ b/arch/powerpc/kernel/vdso/vdso32.lds.S
@@ -130,6 +130,7 @@ VERSION
 #if defined(CONFIG_PPC64) || !defined(CONFIG_SMP)
 		__kernel_getcpu;
 #endif
+		__kernel_getrandom;
 
 	local: *;
 	};
diff --git a/arch/powerpc/kernel/vdso/vdso64.lds.S b/arch/powerpc/kernel/vdso/vdso64.lds.S
index 400819258c06..9481e4b892ed 100644
--- a/arch/powerpc/kernel/vdso/vdso64.lds.S
+++ b/arch/powerpc/kernel/vdso/vdso64.lds.S
@@ -123,6 +123,7 @@ VERSION
 		__kernel_sigtramp_rt64;
 		__kernel_getcpu;
 		__kernel_time;
+		__kernel_getrandom;
 
 	local: *;
 	};
diff --git a/arch/powerpc/kernel/vdso/vgetrandom-chacha.S b/arch/powerpc/kernel/vdso/vgetrandom-chacha.S
new file mode 100644
index 000000000000..5375bc5807e1
--- /dev/null
+++ b/arch/powerpc/kernel/vdso/vgetrandom-chacha.S
@@ -0,0 +1,297 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/ppc_asm.h>
+
+.macro quarterround4 a1 b1 c1 d1 a2 b2 c2 d2 a3 b3 c3 d3 a4 b4 c4 d4
+	add	\a1, \a1, \b1
+	add	\a2, \a2, \b2
+	add	\a3, \a3, \b3
+	add	\a4, \a4, \b4
+	xor	\d1, \d1, \a1
+	xor	\d2, \d2, \a2
+	xor	\d3, \d3, \a3
+	xor	\d4, \d4, \a4
+	rotlwi	\d1, \d1, 16
+	rotlwi	\d2, \d2, 16
+	rotlwi	\d3, \d3, 16
+	rotlwi	\d4, \d4, 16
+	add	\c1, \c1, \d1
+	add	\c2, \c2, \d2
+	add	\c3, \c3, \d3
+	add	\c4, \c4, \d4
+	xor	\b1, \b1, \c1
+	xor	\b2, \b2, \c2
+	xor	\b3, \b3, \c3
+	xor	\b4, \b4, \c4
+	rotlwi	\b1, \b1, 12
+	rotlwi	\b2, \b2, 12
+	rotlwi	\b3, \b3, 12
+	rotlwi	\b4, \b4, 12
+	add	\a1, \a1, \b1
+	add	\a2, \a2, \b2
+	add	\a3, \a3, \b3
+	add	\a4, \a4, \b4
+	xor	\d1, \d1, \a1
+	xor	\d2, \d2, \a2
+	xor	\d3, \d3, \a3
+	xor	\d4, \d4, \a4
+	rotlwi	\d1, \d1, 8
+	rotlwi	\d2, \d2, 8
+	rotlwi	\d3, \d3, 8
+	rotlwi	\d4, \d4, 8
+	add	\c1, \c1, \d1
+	add	\c2, \c2, \d2
+	add	\c3, \c3, \d3
+	add	\c4, \c4, \d4
+	xor	\b1, \b1, \c1
+	xor	\b2, \b2, \c2
+	xor	\b3, \b3, \c3
+	xor	\b4, \b4, \c4
+	rotlwi	\b1, \b1, 7
+	rotlwi	\b2, \b2, 7
+	rotlwi	\b3, \b3, 7
+	rotlwi	\b4, \b4, 7
+.endm
+
+#define QUARTERROUND4(a1,b1,c1,d1,a2,b2,c2,d2,a3,b3,c3,d3,a4,b4,c4,d4) \
+	quarterround4 16+a1 16+b1 16+c1 16+d1 16+a2 16+b2 16+c2 16+d2 \
+		      16+a3 16+b3 16+c3 16+d3 16+a4 16+b4 16+c4 16+d4
+
+/*
+ * Very basic 32 bits implementation of ChaCha20. Produces a given positive number
+ * of blocks of output with a nonce of 0, taking an input key and 8-byte
+ * counter. Importantly does not spill to the stack. Its arguments are:
+ *
+ *	r3: output bytes
+ *	r4: 32-byte key input
+ *	r5: 8-byte counter input/output
+ *	r6: number of 64-byte blocks to write to output
+ *
+ *	r0: counter of blocks (initialised with r6)
+ *	r4: Value '4' after key has been read.
+ *	r6-r13: key
+ *	r14-r15 : counter
+ *	r16-r31 : state
+ */
+SYM_FUNC_START(__arch_chacha20_blocks_nostack)
+#ifdef __powerpc64__
+	std	r14,-144(r1)
+	std	r15,-136(r1)
+	std	r16,-128(r1)
+	std	r17,-120(r1)
+	std	r18,-112(r1)
+	std	r19,-104(r1)
+	std	r20,-96(r1)
+	std	r21,-88(r1)
+	std	r22,-80(r1)
+	std	r23,-72(r1)
+	std	r24,-64(r1)
+	std	r25,-56(r1)
+	std	r26,-48(r1)
+	std	r27,-40(r1)
+	std	r28,-32(r1)
+	std	r29,-24(r1)
+	std	r30,-16(r1)
+	std	r31,-8(r1)
+#else
+	stwu	r1, -96(r1)
+#if defined(CONFIG_CPU_LITTLE_ENDIAN)
+	stw	r14,24(r1)
+	stw	r15,28(r1)
+	stw	r16,32(r1)
+	stw	r17,36(r1)
+	stw	r18,40(r1)
+	stw	r19,44(r1)
+	stw	r20,48(r1)
+	stw	r21,52(r1)
+	stw	r22,56(r1)
+	stw	r23,60(r1)
+	stw	r24,64(r1)
+	stw	r25,68(r1)
+	stw	r26,72(r1)
+	stw	r27,76(r1)
+	stw	r28,80(r1)
+	stw	r29,84(r1)
+	stw	r30,88(r1)
+	stw	r31,92(r1)
+#else
+	stmw	r14, 24(r1)
+#endif
+#endif
+	mr	r0, r6
+
+	li	r31, 4
+
+	LWZX_LE	r6, 0, r4
+	LWZX_LE	r7, r31, r4
+	addi	r4, r4, 8
+	LWZX_LE	r8, 0, r4
+	LWZX_LE	r9, r31, r4
+	addi	r4, r4, 8
+	LWZX_LE	r10, 0, r4
+	LWZX_LE	r11, r31, r4
+	addi	r4, r4, 8
+	LWZX_LE	r12, 0, r4
+	LWZX_LE	r13, r31, r4
+
+	li	r4, 4
+
+	LWZX_LE	r14, 0, r5
+	LWZX_LE	r15, r4, r5
+#ifdef __powerpc64__
+	rldimi	r14, r15, 32, 0
+#endif
+.Lblock:
+	li	r31, 10
+
+	lis	r16, 0x6170
+	lis	r17, 0x3320
+	lis	r18, 0x7962
+	lis	r19, 0x6b20
+	addi	r16, r16, 0x7865
+	addi	r17, r17, 0x646e
+	addi	r18, r18, 0x2d32
+	addi	r19, r19, 0x6574
+
+	mtctr	r31
+
+	mr	r20, r6
+	mr	r21, r7
+	mr	r22, r8
+	mr	r23, r9
+	mr	r24, r10
+	mr	r25, r11
+	mr	r26, r12
+	mr	r27, r13
+
+	mr	r28, r14
+	mr	r29, r15
+	li	r30, 0
+	li	r31, 0
+
+.Lpermute:
+	QUARTERROUND4( 0, 4, 8,12, 1, 5, 9,13, 2, 6,10,14, 3, 7,11,15)
+	QUARTERROUND4( 0, 5,10,15, 1, 6,11,12, 2, 7, 8,13, 3, 4, 9,14)
+
+	bdnz	.Lpermute
+
+	addis	r16, r16, 0x6170
+	addis	r17, r17, 0x3320
+	addis	r18, r18, 0x7962
+	addis	r19, r19, 0x6b20
+	addi	r16, r16, 0x7865
+	addi	r17, r17, 0x646e
+	addi	r18, r18, 0x2d32
+	addi	r19, r19, 0x6574
+
+	add	r20, r20, r6
+	add	r21, r21, r7
+	add	r22, r22, r8
+	add	r23, r23, r9
+	add	r24, r24, r10
+	add	r25, r25, r11
+	add	r26, r26, r12
+	add	r27, r27, r13
+
+	add	r28, r28, r14
+	add	r29, r29, r15
+
+	STWX_LE	r16, 0, r3
+	STWX_LE	r17, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r18, 0, r3
+	STWX_LE	r19, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r20, 0, r3
+	STWX_LE	r21, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r22, 0, r3
+	STWX_LE	r23, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r24, 0, r3
+	STWX_LE	r25, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r26, 0, r3
+	STWX_LE	r27, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r28, 0, r3
+	STWX_LE	r29, r4, r3
+	addi	r3, r3, 8
+	STWX_LE	r30, 0, r3
+	STWX_LE	r31, r4, r3
+	addi	r3, r3, 8
+
+#ifdef __powerpc64__
+	addi	r14, r14, 1
+	srdi	r15, r14, 32
+#else
+	addic	r14, r14, 1
+	addze	r15, r15
+#endif
+
+	subic.	r0, r0, 1	/* subi. can't use r0 as source */
+	bne	.Lblock
+
+	STWX_LE	r14, 0, r5
+	STWX_LE	r15, r4, r5
+
+	li	r6, 0
+	li	r7, 0
+	li	r8, 0
+	li	r9, 0
+	li	r10, 0
+	li	r11, 0
+	li	r12, 0
+	li	r13, 0
+
+#ifdef __powerpc64__
+	ld	r14,-144(r1)
+	ld	r15,-136(r1)
+	ld	r16,-128(r1)
+	ld	r17,-120(r1)
+	ld	r18,-112(r1)
+	ld	r19,-104(r1)
+	ld	r20,-96(r1)
+	ld	r21,-88(r1)
+	ld	r22,-80(r1)
+	ld	r23,-72(r1)
+	ld	r24,-64(r1)
+	ld	r25,-56(r1)
+	ld	r26,-48(r1)
+	ld	r27,-40(r1)
+	ld	r28,-32(r1)
+	ld	r29,-24(r1)
+	ld	r30,-16(r1)
+	ld	r31,-8(r1)
+#else
+#if defined(CONFIG_CPU_LITTLE_ENDIAN)
+	lwz	r14,24(r1)
+	lwz	r15,28(r1)
+	lwz	r16,32(r1)
+	lwz	r17,36(r1)
+	lwz	r18,40(r1)
+	lwz	r19,44(r1)
+	lwz	r20,48(r1)
+	lwz	r21,52(r1)
+	lwz	r22,56(r1)
+	lwz	r23,60(r1)
+	lwz	r24,64(r1)
+	lwz	r25,68(r1)
+	lwz	r26,72(r1)
+	lwz	r27,76(r1)
+	lwz	r28,80(r1)
+	lwz	r29,84(r1)
+	lwz	r30,88(r1)
+	lwz	r31,92(r1)
+#else
+	lmw	r14, 24(r1)
+#endif
+	addi	r1, r1, 96
+#endif
+	blr
+SYM_FUNC_END(__arch_chacha20_blocks_nostack)
diff --git a/arch/powerpc/kernel/vdso/vgetrandom.c b/arch/powerpc/kernel/vdso/vgetrandom.c
new file mode 100644
index 000000000000..5f855d45fb7b
--- /dev/null
+++ b/arch/powerpc/kernel/vdso/vgetrandom.c
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Powerpc userspace implementation of getrandom()
+ *
+ * Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
+ */
+#include <linux/time.h>
+#include <linux/types.h>
+
+ssize_t __c_kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state,
+			     size_t opaque_len, const struct vdso_rng_data *vd)
+{
+	return __cvdso_getrandom_data(vd, buffer, len, flags, opaque_state, opaque_len);
+}
-- 
2.44.0

[PATCH v2 12/17] selftests: vdso: Fix powerpc64 vdso_config

[Christophe Leroy]

__powerpc__ is also defined on powerpc64 so __powerpc64__ needs to be
checked first.

Fixes: 693f5ca08ca0 ("kselftest: Extend vDSO selftest")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/testing/selftests/vDSO/vdso_config.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/vDSO/vdso_config.h b/tools/testing/selftests/vDSO/vdso_config.h
index 7b543e7f04d7..00bfed6e4922 100644
--- a/tools/testing/selftests/vDSO/vdso_config.h
+++ b/tools/testing/selftests/vDSO/vdso_config.h
@@ -18,13 +18,13 @@
 #elif defined(__aarch64__)
 #define VDSO_VERSION		3
 #define VDSO_NAMES		0
-#elif defined(__powerpc__)
+#elif defined(__powerpc64__)
 #define VDSO_VERSION		1
 #define VDSO_NAMES		0
-#define VDSO_32BIT		1
-#elif defined(__powerpc64__)
+#elif defined(__powerpc__)
 #define VDSO_VERSION		1
 #define VDSO_NAMES		0
+#define VDSO_32BIT		1
 #elif defined (__s390__)
 #define VDSO_VERSION		2
 #define VDSO_NAMES		0
-- 
2.44.0

[PATCH v2 13/17] selftests: vdso: Don't hard-code location of vDSO sources

[Christophe Leroy]

Architectures use different location for vDSO sources:
	arch/mips/vdso
	arch/sparc/vdso
	arch/arm64/kernel/vdso
	arch/riscv/kernel/vdso
	arch/csky/kernel/vdso
	arch/x86/um/vdso
	arch/x86/entry/vdso
	arch/powerpc/kernel/vdso
	arch/arm/vdso
	arch/loongarch/vdso

Don't hard-code vdso sources location in selftest Makefile,
instead create a vdso/ symbolic link in tools/arch/$arch/ and
update Makefile accordingly.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/arch/x86/vdso                   | 1 +
 tools/testing/selftests/vDSO/Makefile | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
 create mode 120000 tools/arch/x86/vdso

diff --git a/tools/arch/x86/vdso b/tools/arch/x86/vdso
new file mode 120000
index 000000000000..7eb962fd3454
--- /dev/null
+++ b/tools/arch/x86/vdso
@@ -0,0 +1 @@
+../../../arch/x86/entry/vdso/
\ No newline at end of file
diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index 3de8e7e052ae..c9a819cacbf2 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/tools/testing/selftests/vDSO/Makefile
@@ -40,7 +40,7 @@ $(OUTPUT)/vdso_test_getrandom: parse_vdso.c
 $(OUTPUT)/vdso_test_getrandom: CFLAGS += -isystem $(top_srcdir)/tools/include \
                                          -isystem $(top_srcdir)/include/uapi
 
-$(OUTPUT)/vdso_test_chacha: $(top_srcdir)/arch/$(ARCH)/entry/vdso/vgetrandom-chacha.S
+$(OUTPUT)/vdso_test_chacha: $(top_srcdir)/tools/arch/$(ARCH)/vdso/vgetrandom-chacha.S
 $(OUTPUT)/vdso_test_chacha: CFLAGS += -idirafter $(top_srcdir)/tools/include \
                                       -isystem $(top_srcdir)/arch/$(ARCH)/include \
                                       -isystem $(top_srcdir)/include \
-- 
2.44.0

[PATCH v2 14/17] selftests: vdso: Make test_vdso_getrandom look for the right vDSO function

[Christophe Leroy]

Don't hard-code x86 specific names, use vdso_config definitions
to find the correct function matching the architecture.

Add random VDSO function names in names[][]. Remove the #ifdef
CONFIG_VDSO32, having the name there all the time is harmless
and guaranties a steady index for following strings.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/testing/selftests/vDSO/vdso_config.h         | 8 +++-----
 tools/testing/selftests/vDSO/vdso_test_getrandom.c | 8 ++++++--
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/vDSO/vdso_config.h b/tools/testing/selftests/vDSO/vdso_config.h
index 00bfed6e4922..740ce8c98d2e 100644
--- a/tools/testing/selftests/vDSO/vdso_config.h
+++ b/tools/testing/selftests/vDSO/vdso_config.h
@@ -68,16 +68,15 @@ static const char *versions[7] = {
 	"LINUX_5.10"
 };
 
-static const char *names[2][6] = {
+static const char *names[2][7] = {
 	{
 		"__kernel_gettimeofday",
 		"__kernel_clock_gettime",
 		"__kernel_time",
 		"__kernel_clock_getres",
 		"__kernel_getcpu",
-#if defined(VDSO_32BIT)
 		"__kernel_clock_gettime64",
-#endif
+		"__kernel_getrandom",
 	},
 	{
 		"__vdso_gettimeofday",
@@ -85,9 +84,8 @@ static const char *names[2][6] = {
 		"__vdso_time",
 		"__vdso_clock_getres",
 		"__vdso_getcpu",
-#if defined(VDSO_32BIT)
 		"__vdso_clock_gettime64",
-#endif
+		"__vdso_getrandom",
 	},
 };
 
diff --git a/tools/testing/selftests/vDSO/vdso_test_getrandom.c b/tools/testing/selftests/vDSO/vdso_test_getrandom.c
index 05122425a873..02bcffc23e0c 100644
--- a/tools/testing/selftests/vDSO/vdso_test_getrandom.c
+++ b/tools/testing/selftests/vDSO/vdso_test_getrandom.c
@@ -21,6 +21,7 @@
 
 #include "../kselftest.h"
 #include "parse_vdso.h"
+#include "vdso_config.h"
 
 #ifndef timespecsub
 #define	timespecsub(tsp, usp, vsp)					\
@@ -107,6 +108,9 @@ static void vgetrandom_put_state(void *state)
 
 static void vgetrandom_init(void)
 {
+	const char *version = versions[VDSO_VERSION];
+	const char **name = (const char **)&names[VDSO_NAMES];
+
 	if (pthread_key_create(&grnd_ctx.key, vgetrandom_put_state) != 0)
 		return;
 	unsigned long sysinfo_ehdr = getauxval(AT_SYSINFO_EHDR);
@@ -115,9 +119,9 @@ static void vgetrandom_init(void)
 		exit(KSFT_SKIP);
 	}
 	vdso_init_from_sysinfo_ehdr(sysinfo_ehdr);
-	grnd_ctx.fn = (__typeof__(grnd_ctx.fn))vdso_sym("LINUX_2.6", "__vdso_getrandom");
+	grnd_ctx.fn = (__typeof__(grnd_ctx.fn))vdso_sym(version, name[6]);
 	if (!grnd_ctx.fn) {
-		printf("__vdso_getrandom is missing!\n");
+		printf("%s is missing!\n", name[6]);
 		exit(KSFT_FAIL);
 	}
 	if (grnd_ctx.fn(NULL, 0, 0, &grnd_ctx.params, ~0UL) != 0) {
-- 
2.44.0

[PATCH v2 15/17] selftests: vdso: Fix build of test_vdso_chacha

[Christophe Leroy]

Building test_vdso_chacha on powerpc leads to following issue:

  In file included from /home/chleroy/linux-powerpc/include/linux/limits.h:7,
                   from /opt/powerpc64-e5500--glibc--stable-2024.02-1/powerpc64-buildroot-linux-gnu/sysroot/usr/include/bits/local_lim.h:38,
                   from /opt/powerpc64-e5500--glibc--stable-2024.02-1/powerpc64-buildroot-linux-gnu/sysroot/usr/include/bits/posix1_lim.h:161,
                   from /opt/powerpc64-e5500--glibc--stable-2024.02-1/powerpc64-buildroot-linux-gnu/sysroot/usr/include/limits.h:195,
                   from /opt/powerpc64-e5500--glibc--stable-2024.02-1/lib/gcc/powerpc64-buildroot-linux-gnu/12.3.0/include-fixed/limits.h:203,
                   from /opt/powerpc64-e5500--glibc--stable-2024.02-1/lib/gcc/powerpc64-buildroot-linux-gnu/12.3.0/include-fixed/syslimits.h:7,
                   from /opt/powerpc64-e5500--glibc--stable-2024.02-1/lib/gcc/powerpc64-buildroot-linux-gnu/12.3.0/include-fixed/limits.h:34,
                   from /tmp/sodium/usr/local/include/sodium/export.h:7,
                   from /tmp/sodium/usr/local/include/sodium/crypto_stream_chacha20.h:14,
                   from vdso_test_chacha.c:6:
  /opt/powerpc64-e5500--glibc--stable-2024.02-1/powerpc64-buildroot-linux-gnu/sysroot/usr/include/bits/xopen_lim.h:99:6: error: missing binary operator before token "("
     99 | # if INT_MAX == 32767
        |      ^~~~~~~
  /opt/powerpc64-e5500--glibc--stable-2024.02-1/powerpc64-buildroot-linux-gnu/sysroot/usr/include/bits/xopen_lim.h:102:7: error: missing binary operator before token "("
    102 | #  if INT_MAX == 2147483647
        |       ^~~~~~~
  /opt/powerpc64-e5500--glibc--stable-2024.02-1/powerpc64-buildroot-linux-gnu/sysroot/usr/include/bits/xopen_lim.h:126:6: error: missing binary operator before token "("
    126 | # if LONG_MAX == 2147483647
        |      ^~~~~~~~

This is due to kernel include/linux/limits.h being included instead of libc's
limits.h

This is because directory include/ is added through option -isystem so it goes
prior to glibc's include directory.

Replace -isystem by -idirafter

But this implies that now tools/include/linux/linkage.h is
included instead of include/linux/linkage.h, so define a stub
for SYM_FUNC_START() and SYM_FUNC_END().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/include/linux/linkage.h         | 4 ++++
 tools/testing/selftests/vDSO/Makefile | 4 ++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/include/linux/linkage.h b/tools/include/linux/linkage.h
index bc763d500262..a48ff086899c 100644
--- a/tools/include/linux/linkage.h
+++ b/tools/include/linux/linkage.h
@@ -1,4 +1,8 @@
 #ifndef _TOOLS_INCLUDE_LINUX_LINKAGE_H
 #define _TOOLS_INCLUDE_LINUX_LINKAGE_H
 
+#define SYM_FUNC_START(x) .globl x; x:
+
+#define SYM_FUNC_END(x)
+
 #endif /* _TOOLS_INCLUDE_LINUX_LINKAGE_H */
diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index c9a819cacbf2..10ffdda3f2fa 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/tools/testing/selftests/vDSO/Makefile
@@ -42,7 +42,7 @@ $(OUTPUT)/vdso_test_getrandom: CFLAGS += -isystem $(top_srcdir)/tools/include \
 
 $(OUTPUT)/vdso_test_chacha: $(top_srcdir)/tools/arch/$(ARCH)/vdso/vgetrandom-chacha.S
 $(OUTPUT)/vdso_test_chacha: CFLAGS += -idirafter $(top_srcdir)/tools/include \
-                                      -isystem $(top_srcdir)/arch/$(ARCH)/include \
-                                      -isystem $(top_srcdir)/include \
+                                      -idirafter $(top_srcdir)/arch/$(ARCH)/include \
+                                      -idirafter $(top_srcdir)/include \
                                       -D__ASSEMBLY__ -DBULID_VDSO -DCONFIG_FUNCTION_ALIGNMENT=0 \
                                       -Wa,--noexecstack $(SODIUM)
-- 
2.44.0

[PATCH v2 16/17] selftests: vdso: Make VDSO function call more generic

[Christophe Leroy]

On powerpc, a call to a VDSO function is not a standard C function
call. Unlike x86 that returns a negated error code in case of an
error, powerpc sets CR[SO] and returns the error code as a
positive value.

So use a macro called VDSO_CALL() which takes a pointer to the
function to call, the number of arguments and the arguments.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/testing/selftests/vDSO/vdso_call.h           | 12 ++++++++++++
 tools/testing/selftests/vDSO/vdso_test_getrandom.c |  3 ++-
 2 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/vDSO/vdso_call.h

diff --git a/tools/testing/selftests/vDSO/vdso_call.h b/tools/testing/selftests/vDSO/vdso_call.h
new file mode 100644
index 000000000000..ca5db2220925
--- /dev/null
+++ b/tools/testing/selftests/vDSO/vdso_call.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Macro to call vDSO functions
+ *
+ * Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
+ */
+#ifndef __VDSO_CALL_H__
+#define __VDSO_CALL_H__
+
+#define VDSO_CALL(fn, nr, args...)	fn(args)
+
+#endif
diff --git a/tools/testing/selftests/vDSO/vdso_test_getrandom.c b/tools/testing/selftests/vDSO/vdso_test_getrandom.c
index 02bcffc23e0c..16ad400721c3 100644
--- a/tools/testing/selftests/vDSO/vdso_test_getrandom.c
+++ b/tools/testing/selftests/vDSO/vdso_test_getrandom.c
@@ -22,6 +22,7 @@
 #include "../kselftest.h"
 #include "parse_vdso.h"
 #include "vdso_config.h"
+#include "vdso_call.h"
 
 #ifndef timespecsub
 #define	timespecsub(tsp, usp, vsp)					\
@@ -147,7 +148,7 @@ static ssize_t vgetrandom(void *buf, size_t len, unsigned long flags)
 			exit(KSFT_FAIL);
 		}
 	}
-	return grnd_ctx.fn(buf, len, flags, state, grnd_ctx.params.size_of_opaque_state);
+	return VDSO_CALL(grnd_ctx.fn, 5, buf, len, flags, state, grnd_ctx.params.size_of_opaque_state);
 }
 
 enum { TRIALS = 25000000, THREADS = 256 };
-- 
2.44.0

[PATCH v2 17/17] selftests: vdso: Add support for vdso_test_random for powerpc

[Christophe Leroy]

Add the necessary symbolic link and tell Makefile to build
vdso_test_random for powerpc.

In makefile, don't use $(uname_M) which is wrong when cross-building
for powerpc on an x86_64.

Implement the required VDSO_CALL macro to correctly handle errors.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/arch/powerpc/vdso                  |  1 +
 tools/testing/selftests/vDSO/Makefile    |  6 ++++
 tools/testing/selftests/vDSO/vdso_call.h | 40 ++++++++++++++++++++++++
 3 files changed, 47 insertions(+)
 create mode 120000 tools/arch/powerpc/vdso

diff --git a/tools/arch/powerpc/vdso b/tools/arch/powerpc/vdso
new file mode 120000
index 000000000000..d31004bf8f55
--- /dev/null
+++ b/tools/arch/powerpc/vdso
@@ -0,0 +1 @@
+../../../arch/powerpc/kernel/vdso/
\ No newline at end of file
diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index 10ffdda3f2fa..7e7c9fd200d3 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/tools/testing/selftests/vDSO/Makefile
@@ -17,6 +17,12 @@ ifneq ($(SODIUM),)
 TEST_GEN_PROGS += vdso_test_chacha
 endif
 endif
+ifeq ($(ARCH),powerpc)
+TEST_GEN_PROGS += vdso_test_getrandom
+ifneq ($(SODIUM),)
+TEST_GEN_PROGS += vdso_test_chacha
+endif
+endif
 
 CFLAGS := -std=gnu99
 
diff --git a/tools/testing/selftests/vDSO/vdso_call.h b/tools/testing/selftests/vDSO/vdso_call.h
index ca5db2220925..2a33c25756dc 100644
--- a/tools/testing/selftests/vDSO/vdso_call.h
+++ b/tools/testing/selftests/vDSO/vdso_call.h
@@ -7,6 +7,46 @@
 #ifndef __VDSO_CALL_H__
 #define __VDSO_CALL_H__
 
+#ifdef __powerpc__
+
+#define LOADARGS_5(fn, __arg1, __arg2, __arg3, __arg4, __arg5) do { 	\
+	_r0 = fn;							\
+	_r3 = (long)__arg1;						\
+	_r4 = (long)__arg2;						\
+	_r5 = (long)__arg3;						\
+	_r6 = (long)__arg4;						\
+	_r7 = (long)__arg5;						\
+} while (0)
+
+#define VDSO_CALL(fn, nr, args...) ({					\
+	register void *_r0 asm ("r0");					\
+	register long _r3 asm ("r3");					\
+	register long _r4 asm ("r4");					\
+	register long _r5 asm ("r5");					\
+	register long _r6 asm ("r6");					\
+	register long _r7 asm ("r7");					\
+	register long _r8 asm ("r8");					\
+	register long _rval asm ("r3");					\
+									\
+	LOADARGS_##nr(fn, args);					\
+									\
+	asm volatile(							\
+		"	mtctr %0\n"					\
+		"	bctrl\n"					\
+		"	bns+	1f\n"					\
+		"	neg	3, 3\n"					\
+		"1:"							\
+		: "+r" (_r0), "=r" (_r3), "+r" (_r4), "+r" (_r5),	\
+		  "+r" (_r6), "+r" (_r7), "+r" (_r8)			\
+		: "r" (_rval)						\
+		: "r9", "r10", "r11", "r12", "cr0", "cr1", "cr5",	\
+		  "cr6", "cr7", "xer", "lr", "ctr", "memory"		\
+	);								\
+	_rval;								\
+})
+
+#else
 #define VDSO_CALL(fn, nr, args...)	fn(args)
+#endif
 
 #endif
-- 
2.44.0

Re: [PATCH v2 00/17] Wire up getrandom() vDSO implementation on powerpc

[Jason A. Donenfeld]

Hi Christophe,

Thanks for this series. There are quite a few preliminary patches in it,
before you get to the PPC part, which fix up general build system or test
harness correctness issues. Since some of those affect all architectures
that are adding vDSO getrandom() support for 6.12, I'm going to take
those into my random.git tree as a fix for 6.11 now, in hopes that the
new archs can mostly go into arch trees without too many tree
interdependencies.

So I'll reply to individual patches for that, mentioning which ones I
extract.

Jason

Re: [PATCH v2 01/17] asm-generic/unaligned.h: Extract common header for vDSO

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:09AM +0200, Christophe Leroy wrote:
>  include/asm-generic/unaligned.h | 11 +----------
>  include/vdso/unaligned.h        | 15 +++++++++++++++
>  2 files changed, 16 insertions(+), 10 deletions(-)
>  create mode 100644 include/vdso/unaligned.h

Do you need to also adjust the `#include <asm/unaligned.h>` inside of
lib/vdso/getrandom.c to instead read `#include <vdso/unaligned.h>`?

Jason

Re: [PATCH v2 03/17] vdso: Add __arch_get_k_vdso_rng_data()

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:11AM +0200, Christophe Leroy wrote:
> _vdso_data is specific to x86 and __arch_get_k_vdso_data() is provided
> so that all architectures can provide the requested pointer.
> 
> Do the same with _vdso_rng_data, provide __arch_get_k_vdso_rng_data()
> and don't use x86 _vdso_rng_data directly.
> 
> Until now vdso/vsyscall.h was only included by time/vsyscall.c but now
> it will also be included in char/random.c, leading to a duplicate
> declaration of _vdso_data and _vdso_rng_data.
> 
> To fix this issue, move declaration in a C file. vma.c looks like the
> most appropriate candidate. Don't need to replace the definitions in
> vsyscall.h by declarations as declarations are already in asm/vvar.h
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> v2: Move x86 DEFINE_VVAR(_vdso_data) and DEFINE_VVAR(_vdso_rng_data) in vma.c

Thanks, this seems sane to me. I'll apply this now to random.git as a
fix; it should have been done this way before and is going to be a
headache to coordinate later.

Jason

Re: [PATCH v2 13/17] selftests: vdso: Don't hard-code location of vDSO sources

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:21AM +0200, Christophe Leroy wrote:
> Architectures use different location for vDSO sources:
> 	arch/mips/vdso
> 	arch/sparc/vdso
> 	arch/arm64/kernel/vdso
> 	arch/riscv/kernel/vdso
> 	arch/csky/kernel/vdso
> 	arch/x86/um/vdso
> 	arch/x86/entry/vdso
> 	arch/powerpc/kernel/vdso
> 	arch/arm/vdso
> 	arch/loongarch/vdso
> 
> Don't hard-code vdso sources location in selftest Makefile,
> instead create a vdso/ symbolic link in tools/arch/$arch/ and
> update Makefile accordingly.

That seems like a good way of handling it. As archs add their
implementations, they can just add the symlink and do no more work. It
will also make review slightly easier: if I don't see the symlink added,
I'll know the submitter didn't actually test their chacha :-P.

I'll take this into my random.git tree now as a fix.

Jason

Re: [PATCH v2 14/17] selftests: vdso: Make test_vdso_getrandom look for the right vDSO function

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:22AM +0200, Christophe Leroy wrote:
> Don't hard-code x86 specific names, use vdso_config definitions
> to find the correct function matching the architecture.
> 
> Add random VDSO function names in names[][]. Remove the #ifdef
> CONFIG_VDSO32, having the name there all the time is harmless
> and guaranties a steady index for following strings.

This is indeed the right way of doing it. Thanks. I'll take this now,
though with one small fixup:

> +	const char *version = versions[VDSO_VERSION];
> +	const char **name = (const char **)&names[VDSO_NAMES];

I'll just do:

        const char *name = names[VDSO_NAMES][6];

Instead of referring to name[6] everywhere after. Seems more straight
forward.

Jason

Re: [PATCH v2 01/17] asm-generic/unaligned.h: Extract common header for vDSO

[Christophe Leroy]

Le 26/08/2024 à 09:20, Jason A. Donenfeld a écrit :
> On Thu, Aug 22, 2024 at 09:13:09AM +0200, Christophe Leroy wrote:
>>   include/asm-generic/unaligned.h | 11 +----------
>>   include/vdso/unaligned.h        | 15 +++++++++++++++
>>   2 files changed, 16 insertions(+), 10 deletions(-)
>>   create mode 100644 include/vdso/unaligned.h
> 
> Do you need to also adjust the `#include <asm/unaligned.h>` inside of
> lib/vdso/getrandom.c to instead read `#include <vdso/unaligned.h>`?

Yes, all adjustments to lib/vdso/getrandom.c are in patch 2.

Christophe

Re: [PATCH v2 15/17] selftests: vdso: Fix build of test_vdso_chacha

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:23AM +0200, Christophe Leroy wrote:
> Replace -isystem by -idirafter
> 
> But this implies that now tools/include/linux/linkage.h is
> included instead of include/linux/linkage.h, so define a stub
> for SYM_FUNC_START() and SYM_FUNC_END().

Thanks! I got step 1, but didn't figure out step 2, and tried to do
things the lazy way instead:

-#include <sodium/crypto_stream_chacha20.h>
 #include <sys/random.h>
 #include <string.h>
 #include <stdint.h>
 #include "../kselftest.h"

 extern void __arch_chacha20_blocks_nostack(uint8_t *dst_bytes, const uint8_t *key, uint32_t *counter, size_t nblocks);
+extern int crypto_stream_chacha20(uint8_t *dst_bytes, uint64_t dst_len, const uint8_t *nonce, const uint8_t *key);


Yours is obviously much better, so I'll queue that up instead.

Re: [PATCH v2 14/17] selftests: vdso: Make test_vdso_getrandom look for the right vDSO function

[LEROY Christophe]

Le 26/08/2024 à 09:28, Jason A. Donenfeld a écrit :
> On Thu, Aug 22, 2024 at 09:13:22AM +0200, Christophe Leroy wrote:
>> Don't hard-code x86 specific names, use vdso_config definitions
>> to find the correct function matching the architecture.
>>
>> Add random VDSO function names in names[][]. Remove the #ifdef
>> CONFIG_VDSO32, having the name there all the time is harmless
>> and guaranties a steady index for following strings.
> 
> This is indeed the right way of doing it. Thanks. I'll take this now,
> though with one small fixup:
> 
>> +	const char *version = versions[VDSO_VERSION];
>> +	const char **name = (const char **)&names[VDSO_NAMES];
> 
> I'll just do:
> 
>          const char *name = names[VDSO_NAMES][6];
> 
> Instead of referring to name[6] everywhere after. Seems more straight
> forward.

Yes you are right that's more straight forward when using only one of 
the names.
I copy-pasted it from the gettimeofday test which uses several names 
from the table.

Christophe

Re: [PATCH v2 16/17] selftests: vdso: Make VDSO function call more generic

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:24AM +0200, Christophe Leroy wrote:
> On powerpc, a call to a VDSO function is not a standard C function
> call. Unlike x86 that returns a negated error code in case of an
> error, powerpc sets CR[SO] and returns the error code as a
> positive value.
> 
> So use a macro called VDSO_CALL() which takes a pointer to the
> function to call, the number of arguments and the arguments.
 
You'll probably want to move to VDSO_CALL() for the whole test suite,
not just the getrandom one, right?

Re: [PATCH v2 04/17] vdso: Add missing c-getrandom-y in Makefile

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:12AM +0200, Christophe Leroy wrote:
> Same as for gettimeofday CVDSO implementation, add c-getrandom-y
> to ease the inclusion of lib/vdso/getrandom.c in architectures
> VDSO builds.

Thanks, seems straight forward. I'll apply this now as a fix.

Re: [PATCH v2 16/17] selftests: vdso: Make VDSO function call more generic

[LEROY Christophe]

Le 26/08/2024 à 09:37, Jason A. Donenfeld a écrit :
> On Thu, Aug 22, 2024 at 09:13:24AM +0200, Christophe Leroy wrote:
>> On powerpc, a call to a VDSO function is not a standard C function
>> call. Unlike x86 that returns a negated error code in case of an
>> error, powerpc sets CR[SO] and returns the error code as a
>> positive value.
>>
>> So use a macro called VDSO_CALL() which takes a pointer to the
>> function to call, the number of arguments and the arguments.
>   
> You'll probably want to move to VDSO_CALL() for the whole test suite,
> not just the getrandom one, right?

Yes indeed, the following needs it as well:

vdso_test_abi.c
vdso_test_getcpu.c
vdso_test_gettimeofday.c
vdso_test_correctness.c

Christophe

Re: [PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:14AM +0200, Christophe Leroy wrote:
> Performing SMP atomic operations on u64 fails on powerpc32.
> 
> Random driver generation is handled as unsigned long not u64,
> see for instance base_cnrg or struct crng.
> 
> Use the same type for vDSO's getrandom as it gets copied
> from the above. This is also in line with the local
> current_generation which is already an unsigned long.

This isn't going to work when 32-bit userspace tries to access a 64-bit
kernel.

I had "fixed" this with a vdso_kernel_ulong type way back in an earlier
version: https://lore.kernel.org/lkml/20240528122352.2485958-5-Jason@zx2c4.com/#Z31include:vdso:types.h

But tglx pointed out in that thread that this actually isn't necessary:

| All of this is pointless because if a 32-bit application runs on a
| 64-bit kernel it has to use the 64-bit 'generation'. So why on earth do
| we need magic here for a 32-bit kernel?
| 
| Just use u64 for both and spare all this voodoo. We're seriously not
| "optimizing" for 32-bit kernels.
|
| All what happens on a 32-bit kernel is that the RNG will store the
| unsigned long (32bit) generation into a 64bit variable:
| 
| 	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
| 
| As the upper 32bit are always zero, there is no issue vs. load store
| tearing at all. So there is zero benefit for this aside of slightly
| "better" user space code when running on a 32-bit kernel. Who cares?

So I just got rid of it and used a u64 as he suggested.

However, there's also an additional reason why it's not worth churning
further over this - because VM_DROPPABLE is 64-bit only (due to flags in
vma bits), likely so is vDSO getrandom() for the time being. So I think
it makes more sense to retool this series to be ppc64, and then if you
really really want 32-bit and can convince folks it matters, then all of
these parts (for example, here, the fact that the smp helper doesn't
want to tear) can be fixed up in a separate series.

Jason

Re: [PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[Christophe Leroy]

Le 26/08/2024 à 09:50, Jason A. Donenfeld a écrit :
> On Thu, Aug 22, 2024 at 09:13:14AM +0200, Christophe Leroy wrote:
>> Performing SMP atomic operations on u64 fails on powerpc32.
>>
>> Random driver generation is handled as unsigned long not u64,
>> see for instance base_cnrg or struct crng.
>>
>> Use the same type for vDSO's getrandom as it gets copied
>> from the above. This is also in line with the local
>> current_generation which is already an unsigned long.
> 
> This isn't going to work when 32-bit userspace tries to access a 64-bit
> kernel.
> 
> I had "fixed" this with a vdso_kernel_ulong type way back in an earlier
> version: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20240528122352.2485958-5-Jason%40zx2c4.com%2F%23Z31include%3Avdso%3Atypes.h&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C41747dd989164267c1cc08dcc5a3c424%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638602554376441761%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=Tf9ShSN6aOOFZ1HymAmHhj0xhQ6BUtHJX95t50gsp9k%3D&reserved=0
> 
> But tglx pointed out in that thread that this actually isn't necessary:
> 
> | All of this is pointless because if a 32-bit application runs on a
> | 64-bit kernel it has to use the 64-bit 'generation'. So why on earth do
> | we need magic here for a 32-bit kernel?
> |
> | Just use u64 for both and spare all this voodoo. We're seriously not
> | "optimizing" for 32-bit kernels.
> |
> | All what happens on a 32-bit kernel is that the RNG will store the
> | unsigned long (32bit) generation into a 64bit variable:
> |
> | 	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
> |
> | As the upper 32bit are always zero, there is no issue vs. load store
> | tearing at all. So there is zero benefit for this aside of slightly
> | "better" user space code when running on a 32-bit kernel. Who cares?
> 
> So I just got rid of it and used a u64 as he suggested.
> 
> However, there's also an additional reason why it's not worth churning
> further over this - because VM_DROPPABLE is 64-bit only (due to flags in
> vma bits), likely so is vDSO getrandom() for the time being. So I think
> it makes more sense to retool this series to be ppc64, and then if you
> really really want 32-bit and can convince folks it matters, then all of
> these parts (for example, here, the fact that the smp helper doesn't
> want to tear) can be fixed up in a separate series.

So yes I really really want it on ppc32 because this is the only type of 
boards I have and this is really were we need getrandom() to be 
optimised, indeed ppc64 was sherry-on-the-cake in my series, I just 
added it because it was easy to do after doing ppc32.

Christophe

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:13AM +0200, Christophe Leroy wrote:
> With the current implementation, __cvdso_getrandom_data() calls
> memset(), which is unexpected in the VDSO.
> 
> Rewrite opaque data initialisation to avoid memset().

I think of the various ways I've seen of fixing this -- e.g. adding a
memset() arch-by-arch -- this is the cleanest and simplest. I'll add
this as a fix to random.git now.

Jason

Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Jason A. Donenfeld]

On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index 0c92db84469d..6e4f8fae3ce9 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -5,6 +5,7 @@
>  #include <asm/clocksource.h>
>  #include <asm/pvclock-abi.h>
>  
> +struct timespec64;
>  /* some helper functions for xen and kvm pv clock sources */
>  u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
>  u64 pvclock_clocksource_read_nowd(struct pvclock_vcpu_time_info *src);

This change isn't mentioned in the commit message and could probably
benefit from doing so.

> diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
> index b230f0b10832..cab153c5f9be 100644
> --- a/lib/vdso/getrandom.c
> +++ b/lib/vdso/getrandom.c
> @@ -3,15 +3,13 @@
>   * Copyright (C) 2022-2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
>   */
>  
> -#include <linux/cache.h>
> -#include <linux/kernel.h>
> -#include <linux/time64.h>
> +#include <linux/minmax.h>
>  #include <vdso/datapage.h>
>  #include <vdso/getrandom.h>
> +#include <vdso/unaligned.h>

Ah, that's where you do it. Ignore my comment on the previous commit,
then.

>  #include <asm/vdso/getrandom.h>
> -#include <asm/vdso/vsyscall.h>
> -#include <asm/unaligned.h>
>  #include <uapi/linux/mman.h>
> +#include <uapi/linux/random.h>
>  
>  #define MEMCPY_AND_ZERO_SRC(type, dst, src, len) do {				\
>  	while (len >= sizeof(type)) {						\
> @@ -23,6 +21,9 @@
>  	}									\
>  } while (0)
>  
> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))

If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
instead of _PAGE_SIZE? But if that's the case, why not put the vdso
definition of PAGE_SIZE into some vdso header included by this file?

Re: [PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[Jason A. Donenfeld]

On Mon, Aug 26, 2024 at 10:01:17AM +0200, Christophe Leroy wrote:
> 
> 
> Le 26/08/2024 à 09:50, Jason A. Donenfeld a écrit :
> > On Thu, Aug 22, 2024 at 09:13:14AM +0200, Christophe Leroy wrote:
> >> Performing SMP atomic operations on u64 fails on powerpc32.
> >>
> >> Random driver generation is handled as unsigned long not u64,
> >> see for instance base_cnrg or struct crng.
> >>
> >> Use the same type for vDSO's getrandom as it gets copied
> >> from the above. This is also in line with the local
> >> current_generation which is already an unsigned long.
> > 
> > This isn't going to work when 32-bit userspace tries to access a 64-bit
> > kernel.
> > 
> > I had "fixed" this with a vdso_kernel_ulong type way back in an earlier
> > version: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20240528122352.2485958-5-Jason%40zx2c4.com%2F%23Z31include%3Avdso%3Atypes.h&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C41747dd989164267c1cc08dcc5a3c424%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638602554376441761%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=Tf9ShSN6aOOFZ1HymAmHhj0xhQ6BUtHJX95t50gsp9k%3D&reserved=0
> > 
> > But tglx pointed out in that thread that this actually isn't necessary:
> > 
> > | All of this is pointless because if a 32-bit application runs on a
> > | 64-bit kernel it has to use the 64-bit 'generation'. So why on earth do
> > | we need magic here for a 32-bit kernel?
> > |
> > | Just use u64 for both and spare all this voodoo. We're seriously not
> > | "optimizing" for 32-bit kernels.
> > |
> > | All what happens on a 32-bit kernel is that the RNG will store the
> > | unsigned long (32bit) generation into a 64bit variable:
> > |
> > | 	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
> > |
> > | As the upper 32bit are always zero, there is no issue vs. load store
> > | tearing at all. So there is zero benefit for this aside of slightly
> > | "better" user space code when running on a 32-bit kernel. Who cares?
> > 
> > So I just got rid of it and used a u64 as he suggested.
> > 
> > However, there's also an additional reason why it's not worth churning
> > further over this - because VM_DROPPABLE is 64-bit only (due to flags in
> > vma bits), likely so is vDSO getrandom() for the time being. So I think
> > it makes more sense to retool this series to be ppc64, and then if you
> > really really want 32-bit and can convince folks it matters, then all of
> > these parts (for example, here, the fact that the smp helper doesn't
> > want to tear) can be fixed up in a separate series.
> 
> So yes I really really want it on ppc32 because this is the only type of 
> boards I have and this is really were we need getrandom() to be 
> optimised, indeed ppc64 was sherry-on-the-cake in my series, I just 
> added it because it was easy to do after doing ppc32.

I saw that you did in fact find a bit on ppc32 for VM_DROPPABLE. So it
looks at least possible. Because of this generation counter business, I
still think it might make sense to do in two steps, though, first doing
64-bit, and then doing 32-bit after.

As for the generation counter error you're seeing, I guess what we want
is smp_store_release memory ordering semantics, but letting tearing
happen (since the upper 32-bits will be zero anyway). I'm not sure the
best way to do this, whether it's a new helper, or doing a WRITE_ONCE
together with an smp barrier, or what. But I imagine it's something like
that.

Jason

Re: [PATCH v2 00/17] Wire up getrandom() vDSO implementation on powerpc

[Jason A. Donenfeld]

On Mon, Aug 26, 2024 at 09:19:22AM +0200, Jason A. Donenfeld wrote:
> Hi Christophe,
> 
> Thanks for this series. There are quite a few preliminary patches in it,
> before you get to the PPC part, which fix up general build system or test
> harness correctness issues. Since some of those affect all architectures
> that are adding vDSO getrandom() support for 6.12, I'm going to take
> those into my random.git tree as a fix for 6.11 now, in hopes that the
> new archs can mostly go into arch trees without too many tree
> interdependencies.
> 
> So I'll reply to individual patches for that, mentioning which ones I
> extract.

I've committed a bunch of these to:

    https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/log/

For a v3, if you rebase on there, that'd make things easier for me to
keep picking patches that I intend to send out for 6.11-rc6 later this
week. And then hopefully your 6.12 ppc implementation can just go in via
the ppc tree with my eventual ack on the crypto part, without needing
these interdependencies.

Jason

Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Christophe Leroy]

Le 26/08/2024 à 10:07, Jason A. Donenfeld a écrit :
> On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
>>   
>> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
>> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))
> 
> If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
> instead of _PAGE_SIZE? But if that's the case, why not put the vdso
> definition of PAGE_SIZE into some vdso header included by this file?

It was working ok on powerpc but on x86 I got:

   CC      arch/x86/entry/vdso/vgetrandom.o
In file included from arch/x86/entry/vdso/vgetrandom.c:7:
arch/x86/entry/vdso/../../../../lib/vdso/getrandom.c:24: error: 
"PAGE_SIZE" redefined [-Werror]
    24 | #define PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
       |
In file included from ./arch/x86/include/asm/page.h:9,
                  from ./arch/x86/include/asm/thread_info.h:12,
                  from ./include/linux/thread_info.h:60,
                  from ./include/linux/smp.h:118,
                  from ./include/linux/alloc_tag.h:14,
                  from ./include/linux/percpu.h:5,
                  from ./arch/x86/include/asm/msr.h:15,
                  from ./arch/x86/include/asm/vdso/gettimeofday.h:19,
                  from ./include/vdso/datapage.h:164,
                  from 
arch/x86/entry/vdso/../../../../lib/vdso/getrandom.c:7,
                  from arch/x86/entry/vdso/vgetrandom.c:7:
./arch/x86/include/asm/page_types.h:11: note: this is the location of 
the previous definition
    11 | #define PAGE_SIZE  (_AC(1,UL) << PAGE_SHIFT)
       |
In file included from arch/x86/entry/vdso/vgetrandom.c:7:
arch/x86/entry/vdso/../../../../lib/vdso/getrandom.c:25: error: 
"PAGE_MASK" redefined [-Werror]
    25 | #define PAGE_MASK (~(PAGE_SIZE - 1))
       |
In file included from ./arch/x86/include/asm/page.h:9,
                  from ./arch/x86/include/asm/thread_info.h:12,
                  from ./include/linux/thread_info.h:60,
                  from ./include/linux/smp.h:118,
                  from ./include/linux/alloc_tag.h:14,
                  from ./include/linux/percpu.h:5,
                  from ./arch/x86/include/asm/msr.h:15,
                  from ./arch/x86/include/asm/vdso/gettimeofday.h:19,
                  from ./include/vdso/datapage.h:164,
                  from 
arch/x86/entry/vdso/../../../../lib/vdso/getrandom.c:7,
                  from arch/x86/entry/vdso/vgetrandom.c:7:
./arch/x86/include/asm/page_types.h:12: note: this is the location of 
the previous definition
    12 | #define PAGE_MASK  (~(PAGE_SIZE-1))
       |
cc1: all warnings being treated as errors


Christophe

Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Jason A. Donenfeld]

On Mon, Aug 26, 2024 at 10:37:49AM +0200, Christophe Leroy wrote:
> 
> 
> Le 26/08/2024 à 10:07, Jason A. Donenfeld a écrit :
> > On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
> >>   
> >> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
> >> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))
> > 
> > If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
> > instead of _PAGE_SIZE? But if that's the case, why not put the vdso
> > definition of PAGE_SIZE into some vdso header included by this file?
> 
> It was working ok on powerpc but on x86 I got:

Seems like there might be some more fiddling to do, then? Or did you
conclude it's impossible?

Re: [PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[Thomas Gleixner]

On Mon, Aug 26 2024 at 10:01, Christophe Leroy wrote:
> Le 26/08/2024 à 09:50, Jason A. Donenfeld a écrit :
>> But tglx pointed out in that thread that this actually isn't necessary:
>> 
>> | All of this is pointless because if a 32-bit application runs on a
>> | 64-bit kernel it has to use the 64-bit 'generation'. So why on earth do
>> | we need magic here for a 32-bit kernel?
>> |
>> | Just use u64 for both and spare all this voodoo. We're seriously not
>> | "optimizing" for 32-bit kernels.
>> |
>> | All what happens on a 32-bit kernel is that the RNG will store the
>> | unsigned long (32bit) generation into a 64bit variable:
>> |
>> | 	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
>> |
>> | As the upper 32bit are always zero, there is no issue vs. load store
>> | tearing at all. So there is zero benefit for this aside of slightly
>> | "better" user space code when running on a 32-bit kernel. Who cares?
>> 
>> So I just got rid of it and used a u64 as he suggested.
>> 
>> However, there's also an additional reason why it's not worth churning
>> further over this - because VM_DROPPABLE is 64-bit only (due to flags in
>> vma bits), likely so is vDSO getrandom() for the time being. So I think
>> it makes more sense to retool this series to be ppc64, and then if you
>> really really want 32-bit and can convince folks it matters, then all of
>> these parts (for example, here, the fact that the smp helper doesn't
>> want to tear) can be fixed up in a separate series.
>
> So yes I really really want it on ppc32 because this is the only type of 
> boards I have and this is really were we need getrandom() to be 
> optimised,

For nostalgic reasons?

> indeed ppc64 was sherry-on-the-cake in my series, I just added it
> because it was easy to do after doing ppc32.

The rng problem for ppc32 seems to be:

   smp_store_release(&_vdso_rng_data.generation, next_gen + 1);

right? 

Your proposed type change creates inconsistency for 32-bit userspace
running on 64-bit kernels because the data struct layout changes.

As explained before, there is no problem with store or load tearing on
32bit systems because the generation counter is only 32bit wide. So the
obvious solution is to only update 32 bits on a 32bit kernel:

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -282,7 +282,7 @@ static void crng_reseed(struct work_stru
 	 * is ordered with the write above to base_crng.generation. Pairs with
 	 * the smp_rmb() before the syscall in the vDSO code.
 	 */
-	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
+	smp_store_release((unsigned long *)&_vdso_rng_data.generation, next_gen + 1);
 #endif
 	if (!static_branch_likely(&crng_is_ready))
 		crng_init = CRNG_READY;

Which is perfectly fine on 32-bit independent of endianess because the
user space side does READ_ONCE(data->generation) and the read value is
solely used for comparison so it does not matter at all whether the
generation information is in the upper or the lower 32bit of the u64.

No?

But that's a trivial fix compared to making VM_DROPPABLE work on 32-bit
correclty. :)

Thanks,

        tglx

Re: [PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[Jason A. Donenfeld]

On Mon, Aug 26, 2024 at 11:43:39AM +0200, Thomas Gleixner wrote:
> As explained before, there is no problem with store or load tearing on
> 32bit systems because the generation counter is only 32bit wide. So the
> obvious solution is to only update 32 bits on a 32bit kernel:
> 
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -282,7 +282,7 @@ static void crng_reseed(struct work_stru
>  	 * is ordered with the write above to base_crng.generation. Pairs with
>  	 * the smp_rmb() before the syscall in the vDSO code.
>  	 */
> -	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
> +	smp_store_release((unsigned long *)&_vdso_rng_data.generation, next_gen + 1);
>  #endif
>  	if (!static_branch_likely(&crng_is_ready))
>  		crng_init = CRNG_READY;

That seems like a pretty clean fix.

> But that's a trivial fix compared to making VM_DROPPABLE work on 32-bit
> correclty. :)

My initial response too, and then I noticed he posted this:
https://lore.kernel.org/all/315e3a268b165b6edad7dcb723b0d8a506a56c4e.1724309198.git.christophe.leroy@csgroup.eu/
If that's correct, maybe it's not so bad, at least here. I haven't yet
looked into the details of it.

Jason

Re: [PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32

[kernel test robot]

Hi Christophe,

kernel test robot noticed the following build warnings:

[auto build test WARNING on powerpc/next]
[also build test WARNING on powerpc/fixes shuah-kselftest/next shuah-kselftest/fixes crng-random/master linus/master v6.11-rc5 next-20240823]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Christophe-Leroy/asm-generic-unaligned-h-Extract-common-header-for-vDSO/20240826-103525
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
patch link:    https://lore.kernel.org/r/315e3a268b165b6edad7dcb723b0d8a506a56c4e.1724309198.git.christophe.leroy%40csgroup.eu
patch subject: [PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32
config: x86_64-buildonly-randconfig-002-20240826 (https://download.01.org/0day-ci/archive/20240826/202408261757.D4gOewE9-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240826/202408261757.D4gOewE9-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202408261757.D4gOewE9-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/trace/events/page_ref.h:11,
                    from mm/debug_page_ref.c:6:
>> include/trace/events/mmflags.h:168:5: warning: "VM_DROPPABLE" is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |     ^~~~~~~~~~~~
>> include/trace/events/mmflags.h:168:21: warning: "VM_NONE" is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |                     ^~~~~~~
   In file included from include/trace/events/page_ref.h:11,
                    from include/trace/define_trace.h:95,
                    from include/trace/events/page_ref.h:135:
>> include/trace/events/mmflags.h:168:5: warning: "VM_DROPPABLE" is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |     ^~~~~~~~~~~~
>> include/trace/events/mmflags.h:168:21: warning: "VM_NONE" is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |                     ^~~~~~~
   In file included from include/trace/events/page_ref.h:11,
                    from include/trace/trace_events.h:94,
                    from include/trace/define_trace.h:102:
>> include/trace/events/mmflags.h:169: warning: "IF_HAVE_VM_DROPPABLE" redefined
     169 | # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
         | 
   include/trace/events/mmflags.h:171: note: this is the location of the previous definition
     171 | # define IF_HAVE_VM_DROPPABLE(flag, name)
         | 


vim +/VM_DROPPABLE +168 include/trace/events/mmflags.h

   167	
 > 168	#if VM_DROPPABLE != VM_NONE
 > 169	# define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
   170	#else
   171	# define IF_HAVE_VM_DROPPABLE(flag, name)
   172	#endif
   173	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32

[kernel test robot]

Hi Christophe,

kernel test robot noticed the following build warnings:

[auto build test WARNING on powerpc/next]
[also build test WARNING on powerpc/fixes shuah-kselftest/next shuah-kselftest/fixes linus/master v6.11-rc5 next-20240823]
[cannot apply to crng-random/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Christophe-Leroy/asm-generic-unaligned-h-Extract-common-header-for-vDSO/20240826-103525
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
patch link:    https://lore.kernel.org/r/315e3a268b165b6edad7dcb723b0d8a506a56c4e.1724309198.git.christophe.leroy%40csgroup.eu
patch subject: [PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32
config: x86_64-allyesconfig (https://download.01.org/0day-ci/archive/20240826/202408261734.UAvnH7Mv-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240826/202408261734.UAvnH7Mv-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202408261734.UAvnH7Mv-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from mm/debug_page_ref.c:6:
   In file included from include/trace/events/page_ref.h:11:
   include/trace/events/mmflags.h:168:5: warning: 'VM_DROPPABLE' is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |     ^
   include/trace/events/mmflags.h:168:21: warning: 'VM_NONE' is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |                     ^
   In file included from mm/debug_page_ref.c:6:
   In file included from include/trace/events/page_ref.h:135:
   In file included from include/trace/define_trace.h:95:
   In file included from include/trace/events/page_ref.h:11:
   include/trace/events/mmflags.h:168:5: warning: 'VM_DROPPABLE' is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |     ^
   include/trace/events/mmflags.h:168:21: warning: 'VM_NONE' is not defined, evaluates to 0 [-Wundef]
     168 | #if VM_DROPPABLE != VM_NONE
         |                     ^
   In file included from mm/debug_page_ref.c:6:
   In file included from include/trace/events/page_ref.h:135:
   In file included from include/trace/define_trace.h:102:
   In file included from include/trace/trace_events.h:94:
   In file included from include/trace/events/page_ref.h:11:
>> include/trace/events/mmflags.h:169:10: warning: 'IF_HAVE_VM_DROPPABLE' macro redefined [-Wmacro-redefined]
     169 | # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
         |          ^
   include/trace/events/mmflags.h:171:10: note: previous definition is here
     171 | # define IF_HAVE_VM_DROPPABLE(flag, name)
         |          ^
   5 warnings generated.


vim +/IF_HAVE_VM_DROPPABLE +169 include/trace/events/mmflags.h

7677f7fd8be766 Axel Rasmussen     2021-05-04  167  
41e2c674b334ed Christophe Leroy   2024-08-22 @168  #if VM_DROPPABLE != VM_NONE
9651fcedf7b92d Jason A. Donenfeld 2022-12-08 @169  # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
9651fcedf7b92d Jason A. Donenfeld 2022-12-08  170  #else
9651fcedf7b92d Jason A. Donenfeld 2022-12-08  171  # define IF_HAVE_VM_DROPPABLE(flag, name)
9651fcedf7b92d Jason A. Donenfeld 2022-12-08  172  #endif
9651fcedf7b92d Jason A. Donenfeld 2022-12-08  173  

-- 
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https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2 06/17] vdso: Change getrandom's generation to unsigned long

[LEROY Christophe]

Le 26/08/2024 à 11:43, Thomas Gleixner a écrit :
> On Mon, Aug 26 2024 at 10:01, Christophe Leroy wrote:
>> Le 26/08/2024 à 09:50, Jason A. Donenfeld a écrit :
>>> But tglx pointed out in that thread that this actually isn't necessary:
>>>
>>> | All of this is pointless because if a 32-bit application runs on a
>>> | 64-bit kernel it has to use the 64-bit 'generation'. So why on earth do
>>> | we need magic here for a 32-bit kernel?
>>> |
>>> | Just use u64 for both and spare all this voodoo. We're seriously not
>>> | "optimizing" for 32-bit kernels.
>>> |
>>> | All what happens on a 32-bit kernel is that the RNG will store the
>>> | unsigned long (32bit) generation into a 64bit variable:
>>> |
>>> | 	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
>>> |
>>> | As the upper 32bit are always zero, there is no issue vs. load store
>>> | tearing at all. So there is zero benefit for this aside of slightly
>>> | "better" user space code when running on a 32-bit kernel. Who cares?
>>>
>>> So I just got rid of it and used a u64 as he suggested.
>>>
>>> However, there's also an additional reason why it's not worth churning
>>> further over this - because VM_DROPPABLE is 64-bit only (due to flags in
>>> vma bits), likely so is vDSO getrandom() for the time being. So I think
>>> it makes more sense to retool this series to be ppc64, and then if you
>>> really really want 32-bit and can convince folks it matters, then all of
>>> these parts (for example, here, the fact that the smp helper doesn't
>>> want to tear) can be fixed up in a separate series.
>>
>> So yes I really really want it on ppc32 because this is the only type of
>> boards I have and this is really were we need getrandom() to be
>> optimised,
> 
> For nostalgic reasons?

No nostalgy here. We deliver voice communication systems for air trafic 
control that we are commited to maintain for at least the next 15 years.

The MPC 885 was manufactured by NXP until recently and we have several 
hundreds in stock in case one of our customer needs to extend an 
existing system.

The MPC 8321 is still manufactured by NXP and the boards on new systems 
we deliver use that CPU.

Both are 32 bits powerpc.


> 
>> indeed ppc64 was sherry-on-the-cake in my series, I just added it
>> because it was easy to do after doing ppc32.
> 
> The rng problem for ppc32 seems to be:
> 
>     smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
> 
> right?

right.

> 
> Your proposed type change creates inconsistency for 32-bit userspace
> running on 64-bit kernels because the data struct layout changes.
> 
> As explained before, there is no problem with store or load tearing on
> 32bit systems because the generation counter is only 32bit wide. So the
> obvious solution is to only update 32 bits on a 32bit kernel:
> 
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -282,7 +282,7 @@ static void crng_reseed(struct work_stru
>   	 * is ordered with the write above to base_crng.generation. Pairs with
>   	 * the smp_rmb() before the syscall in the vDSO code.
>   	 */
> -	smp_store_release(&_vdso_rng_data.generation, next_gen + 1);
> +	smp_store_release((unsigned long *)&_vdso_rng_data.generation, next_gen + 1);
>   #endif
>   	if (!static_branch_likely(&crng_is_ready))
>   		crng_init = CRNG_READY;
> 
> Which is perfectly fine on 32-bit independent of endianess because the
> user space side does READ_ONCE(data->generation) and the read value is
> solely used for comparison so it does not matter at all whether the
> generation information is in the upper or the lower 32bit of the u64. >
> No?

Yes that looks ok, it will only require a big fat comment to explain 
that. I'll give it a try.

> 
> But that's a trivial fix compared to making VM_DROPPABLE work on 32-bit
> correclty. :)

Euh ... Ok. What's the problem here ? I have used VM_ARCH_1 which is 
available. Is there more to do ?

Thanks
Christophe

Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Christophe Leroy]

Le 26/08/2024 à 10:58, Jason A. Donenfeld a écrit :
> On Mon, Aug 26, 2024 at 10:37:49AM +0200, Christophe Leroy wrote:
>>
>>
>> Le 26/08/2024 à 10:07, Jason A. Donenfeld a écrit :
>>> On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
>>>>    
>>>> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
>>>> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))
>>>
>>> If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
>>> instead of _PAGE_SIZE? But if that's the case, why not put the vdso
>>> definition of PAGE_SIZE into some vdso header included by this file?
>>
>> It was working ok on powerpc but on x86 I got:
> 
> Seems like there might be some more fiddling to do, then? Or did you
> conclude it's impossible?

Maybe someone who knows x86 in details could helps but after a first 
look I gave up because it looks very x86 specific, indeed that's 
x86/asm/vdso/gettimeofday.h that pulls several x86/asm/ headers , and 
the same type of issue might arise for any new architecture coming in.

For me it looked cleaner to just do as commit cffaefd15a8f ("vdso: Use 
CONFIG_PAGE_SHIFT in vdso/datapage.h") and not use PAGE_SIZE at all. But 
I didn't want to directly use (1UL << CONFIG_PAGE_SHIFT) and (~(1UL << 
(CONFIG_PAGE_SHIFT - 1))) in the code directly hence the new macros with 
a leading underscore to avoid any conflict with existing macros.

Christophe

Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Jason A. Donenfeld]

On Mon, Aug 26, 2024 at 12:45:40PM +0200, Christophe Leroy wrote:
> 
> 
> Le 26/08/2024 à 10:58, Jason A. Donenfeld a écrit :
> > On Mon, Aug 26, 2024 at 10:37:49AM +0200, Christophe Leroy wrote:
> >>
> >>
> >> Le 26/08/2024 à 10:07, Jason A. Donenfeld a écrit :
> >>> On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
> >>>>    
> >>>> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
> >>>> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))
> >>>
> >>> If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
> >>> instead of _PAGE_SIZE? But if that's the case, why not put the vdso
> >>> definition of PAGE_SIZE into some vdso header included by this file?
> >>
> >> It was working ok on powerpc but on x86 I got:
> > 
> > Seems like there might be some more fiddling to do, then? Or did you
> > conclude it's impossible?
> 
> Maybe someone who knows x86 in details could helps but after a first 
> look I gave up because it looks very x86 specific, indeed that's 
> x86/asm/vdso/gettimeofday.h that pulls several x86/asm/ headers , and 
> the same type of issue might arise for any new architecture coming in.
> 
> For me it looked cleaner to just do as commit cffaefd15a8f ("vdso: Use 
> CONFIG_PAGE_SHIFT in vdso/datapage.h") and not use PAGE_SIZE at all. But 
> I didn't want to directly use (1UL << CONFIG_PAGE_SHIFT) and (~(1UL << 
> (CONFIG_PAGE_SHIFT - 1))) in the code directly hence the new macros with 
> a leading underscore to avoid any conflict with existing macros.

If that's the case and you can't sort it out or it's impossible, then it
seems like adding #ifndef PAGE_SIZE, #define... inside of some vdso header
(not inside getrandom.c) would make sense.

Jason

Re: [PATCH v2 02/17] vdso: Clean header inclusion in getrandom

[Thomas Gleixner]

On Mon, Aug 26 2024 at 12:45, Christophe Leroy wrote:
> Le 26/08/2024 à 10:58, Jason A. Donenfeld a écrit :
>> On Mon, Aug 26, 2024 at 10:37:49AM +0200, Christophe Leroy wrote:
>>>
>>>
>>> Le 26/08/2024 à 10:07, Jason A. Donenfeld a écrit :
>>>> On Thu, Aug 22, 2024 at 09:13:10AM +0200, Christophe Leroy wrote:
>>>>>    
>>>>> +#define _PAGE_SIZE (1UL << CONFIG_PAGE_SHIFT)
>>>>> +#define _PAGE_MASK (~(_PAGE_SIZE - 1))
>>>>
>>>> If PAGE_SIZE isn't defined at this point, why not just call it PAGE_SIZE
>>>> instead of _PAGE_SIZE? But if that's the case, why not put the vdso
>>>> definition of PAGE_SIZE into some vdso header included by this file?
>>>
>>> It was working ok on powerpc but on x86 I got:
>> 
>> Seems like there might be some more fiddling to do, then? Or did you
>> conclude it's impossible?
>
> Maybe someone who knows x86 in details could helps but after a first 
> look I gave up because it looks very x86 specific, indeed that's 
> x86/asm/vdso/gettimeofday.h that pulls several x86/asm/ headers , and 
> the same type of issue might arise for any new architecture coming in.

Of course :)

> For me it looked cleaner to just do as commit cffaefd15a8f ("vdso: Use 
> CONFIG_PAGE_SHIFT in vdso/datapage.h") and not use PAGE_SIZE at all. But 
> I didn't want to directly use (1UL << CONFIG_PAGE_SHIFT) and (~(1UL << 
> (CONFIG_PAGE_SHIFT - 1))) in the code directly hence the new macros with 
> a leading underscore to avoid any conflict with existing macros.

#ifndef PAGE_SIZE
# define
#endif

Perhaps?

Thanks,

        tglx

Re: [PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32

[kernel test robot]

Hi Christophe,

kernel test robot noticed the following build warnings:

[auto build test WARNING on powerpc/next]
[also build test WARNING on powerpc/fixes shuah-kselftest/next shuah-kselftest/fixes linus/master v6.11-rc5 next-20240826]
[cannot apply to crng-random/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Christophe-Leroy/asm-generic-unaligned-h-Extract-common-header-for-vDSO/20240826-103525
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
patch link:    https://lore.kernel.org/r/315e3a268b165b6edad7dcb723b0d8a506a56c4e.1724309198.git.christophe.leroy%40csgroup.eu
patch subject: [PATCH v2 07/17] mm: Define VM_DROPPABLE for powerpc/32
config: um-randconfig-r122-20240826 (https://download.01.org/0day-ci/archive/20240827/202408270553.2S5d14Ar-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240827/202408270553.2S5d14Ar-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202408270553.2S5d14Ar-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
   mm/debug_page_ref.c: note: in included file (through include/trace/events/page_ref.h):
>> include/trace/events/mmflags.h:168:5: sparse: sparse: undefined preprocessor identifier 'VM_DROPPABLE'
>> include/trace/events/mmflags.h:168:21: sparse: sparse: undefined preprocessor identifier 'VM_NONE'
   mm/debug_page_ref.c: note: in included file (through include/trace/events/page_ref.h, include/trace/define_trace.h, include/trace/events/page_ref.h):
>> include/trace/events/mmflags.h:168:5: sparse: sparse: undefined preprocessor identifier 'VM_DROPPABLE'
>> include/trace/events/mmflags.h:168:21: sparse: sparse: undefined preprocessor identifier 'VM_NONE'
   mm/debug_page_ref.c: note: in included file (through include/trace/events/page_ref.h, include/trace/trace_events.h, include/trace/define_trace.h, ...):
   include/trace/events/mmflags.h:169:10: sparse: sparse: preprocessor token IF_HAVE_VM_DROPPABLE redefined
   mm/debug_page_ref.c: note: in included file (through include/trace/events/page_ref.h):
   include/trace/events/mmflags.h:171:10: sparse: this was the original definition

vim +/VM_DROPPABLE +168 include/trace/events/mmflags.h

   167	
 > 168	#if VM_DROPPABLE != VM_NONE
   169	# define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
   170	#else
   171	# define IF_HAVE_VM_DROPPABLE(flag, name)
   172	#endif
   173	

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Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Eric Biggers]

On Thu, Aug 22, 2024 at 09:13:13AM +0200, Christophe Leroy wrote:
> With the current implementation, __cvdso_getrandom_data() calls
> memset(), which is unexpected in the VDSO.
> 
> Rewrite opaque data initialisation to avoid memset().
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  lib/vdso/getrandom.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
> index cab153c5f9be..4a56f45141b4 100644
> --- a/lib/vdso/getrandom.c
> +++ b/lib/vdso/getrandom.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include <linux/minmax.h>
> +#include <linux/array_size.h>
>  #include <vdso/datapage.h>
>  #include <vdso/getrandom.h>
>  #include <vdso/unaligned.h>
> @@ -74,11 +75,15 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
>  	u32 counter[2] = { 0 };
>  
>  	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags)) {
> -		*(struct vgetrandom_opaque_params *)opaque_state = (struct vgetrandom_opaque_params) {
> -			.size_of_opaque_state = sizeof(*state),
> -			.mmap_prot = PROT_READ | PROT_WRITE,
> -			.mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS
> -		};
> +		struct vgetrandom_opaque_params *params = opaque_state;
> +		int i;
> +
> +		params->size_of_opaque_state = sizeof(*state);
> +		params->mmap_prot = PROT_READ | PROT_WRITE;
> +		params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
> +		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
> +			params->reserved[i] = 0;
> +
>  		return 0;
>  	}

Is there a compiler flag that could be used to disable the generation of calls
to memset?

- Eric

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Jason A. Donenfeld]

On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> On Thu, Aug 22, 2024 at 09:13:13AM +0200, Christophe Leroy wrote:
> > With the current implementation, __cvdso_getrandom_data() calls
> > memset(), which is unexpected in the VDSO.
> > 
> > Rewrite opaque data initialisation to avoid memset().
> > 
> > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > ---
> >  lib/vdso/getrandom.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> > 
> > diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
> > index cab153c5f9be..4a56f45141b4 100644
> > --- a/lib/vdso/getrandom.c
> > +++ b/lib/vdso/getrandom.c
> > @@ -4,6 +4,7 @@
> >   */
> >  
> >  #include <linux/minmax.h>
> > +#include <linux/array_size.h>
> >  #include <vdso/datapage.h>
> >  #include <vdso/getrandom.h>
> >  #include <vdso/unaligned.h>
> > @@ -74,11 +75,15 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
> >  	u32 counter[2] = { 0 };
> >  
> >  	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags)) {
> > -		*(struct vgetrandom_opaque_params *)opaque_state = (struct vgetrandom_opaque_params) {
> > -			.size_of_opaque_state = sizeof(*state),
> > -			.mmap_prot = PROT_READ | PROT_WRITE,
> > -			.mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS
> > -		};
> > +		struct vgetrandom_opaque_params *params = opaque_state;
> > +		int i;
> > +
> > +		params->size_of_opaque_state = sizeof(*state);
> > +		params->mmap_prot = PROT_READ | PROT_WRITE;
> > +		params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
> > +		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
> > +			params->reserved[i] = 0;
> > +
> >  		return 0;
> >  	}
> 
> Is there a compiler flag that could be used to disable the generation of calls
> to memset?

Apparently not: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90701

-ffreestanding disables the most but still can generate calls to memcpy
and memset, and the bug was closed as "RESOLVED INVALID". Surprising,
but maybe it's one of those "functions are part of language" things.

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> On Thu, Aug 22, 2024 at 09:13:13AM +0200, Christophe Leroy wrote:
> > With the current implementation, __cvdso_getrandom_data() calls
> > memset(), which is unexpected in the VDSO.
> > 
> > Rewrite opaque data initialisation to avoid memset().
> > 
> > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > ---
> >  lib/vdso/getrandom.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> > 
> > diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
> > index cab153c5f9be..4a56f45141b4 100644
> > --- a/lib/vdso/getrandom.c
> > +++ b/lib/vdso/getrandom.c
> > @@ -4,6 +4,7 @@
> >   */
> >  
> >  #include <linux/minmax.h>
> > +#include <linux/array_size.h>
> >  #include <vdso/datapage.h>
> >  #include <vdso/getrandom.h>
> >  #include <vdso/unaligned.h>
> > @@ -74,11 +75,15 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
> >  	u32 counter[2] = { 0 };
> >  
> >  	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags)) {
> > -		*(struct vgetrandom_opaque_params *)opaque_state = (struct vgetrandom_opaque_params) {
> > -			.size_of_opaque_state = sizeof(*state),
> > -			.mmap_prot = PROT_READ | PROT_WRITE,
> > -			.mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS
> > -		};
> > +		struct vgetrandom_opaque_params *params = opaque_state;
> > +		int i;
> > +
> > +		params->size_of_opaque_state = sizeof(*state);
> > +		params->mmap_prot = PROT_READ | PROT_WRITE;
> > +		params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
> > +		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
> > +			params->reserved[i] = 0;
> > +
> >  		return 0;
> >  	}
> 
> Is there a compiler flag that could be used to disable the generation of calls
> to memset?

-fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
what it actually does (and how it avoids your problem, and mostly: learn
what the actual problem *was*!)

Have fun,


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Jason A. Donenfeld]

On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > On Thu, Aug 22, 2024 at 09:13:13AM +0200, Christophe Leroy wrote:
> > > With the current implementation, __cvdso_getrandom_data() calls
> > > memset(), which is unexpected in the VDSO.
> > > 
> > > Rewrite opaque data initialisation to avoid memset().
> > > 
> > > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> > > ---
> > >  lib/vdso/getrandom.c | 15 ++++++++++-----
> > >  1 file changed, 10 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
> > > index cab153c5f9be..4a56f45141b4 100644
> > > --- a/lib/vdso/getrandom.c
> > > +++ b/lib/vdso/getrandom.c
> > > @@ -4,6 +4,7 @@
> > >   */
> > >  
> > >  #include <linux/minmax.h>
> > > +#include <linux/array_size.h>
> > >  #include <vdso/datapage.h>
> > >  #include <vdso/getrandom.h>
> > >  #include <vdso/unaligned.h>
> > > @@ -74,11 +75,15 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
> > >  	u32 counter[2] = { 0 };
> > >  
> > >  	if (unlikely(opaque_len == ~0UL && !buffer && !len && !flags)) {
> > > -		*(struct vgetrandom_opaque_params *)opaque_state = (struct vgetrandom_opaque_params) {
> > > -			.size_of_opaque_state = sizeof(*state),
> > > -			.mmap_prot = PROT_READ | PROT_WRITE,
> > > -			.mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS
> > > -		};
> > > +		struct vgetrandom_opaque_params *params = opaque_state;
> > > +		int i;
> > > +
> > > +		params->size_of_opaque_state = sizeof(*state);
> > > +		params->mmap_prot = PROT_READ | PROT_WRITE;
> > > +		params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
> > > +		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
> > > +			params->reserved[i] = 0;
> > > +
> > >  		return 0;
> > >  	}
> > 
> > Is there a compiler flag that could be used to disable the generation of calls
> > to memset?
> 
> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> what it actually does (and how it avoids your problem, and mostly: learn
> what the actual problem *was*!)

This might help with various loops, but it doesn't help with the matter
that this patch fixes, which is struct initialization. I just tried it
with the arm64 patch to no avail.

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Arnd Bergmann]

On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
>> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
>> > 
>> > Is there a compiler flag that could be used to disable the generation of calls
>> > to memset?
>> 
>> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
>> what it actually does (and how it avoids your problem, and mostly: learn
>> what the actual problem *was*!)
>
> This might help with various loops, but it doesn't help with the matter
> that this patch fixes, which is struct initialization. I just tried it
> with the arm64 patch to no avail.

Maybe -ffreestanding can help here? That should cause the vdso to be built
with the assumption that there is no libc, so it would neither add nor
remove standard library calls. Not sure if that causes other problems,
e.g. if the calling conventions are different.

       Arnd

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Jason A. Donenfeld]

On Wed, Aug 28, 2024 at 2:24 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> >> >
> >> > Is there a compiler flag that could be used to disable the generation of calls
> >> > to memset?
> >>
> >> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> >> what it actually does (and how it avoids your problem, and mostly: learn
> >> what the actual problem *was*!)
> >
> > This might help with various loops, but it doesn't help with the matter
> > that this patch fixes, which is struct initialization. I just tried it
> > with the arm64 patch to no avail.
>
> Maybe -ffreestanding can help here? That should cause the vdso to be built
> with the assumption that there is no libc, so it would neither add nor
> remove standard library calls. Not sure if that causes other problems,
> e.g. if the calling conventions are different.

From https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90701:

| You need -ffreestanding but that is documented to emit memset and
memcpy still.

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

On Wed, Aug 28, 2024 at 01:18:34PM +0200, Jason A. Donenfeld wrote:
> On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> > On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > > > +		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
> > > > +			params->reserved[i] = 0;

This is a loop.  With -ftree-loop-distribute-patterns, the default at
-O2, this is optimised to

    memset(params->reserved, 0, ...);

(which is perfectly fine, since memset is required to be there even
for freestanding environments, this is documented!)

> > -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> > what it actually does (and how it avoids your problem, and mostly: learn
> > what the actual problem *was*!)
> 
> This might help with various loops, but it doesn't help with the matter
> that this patch fixes, which is struct initialization. I just tried it
> with the arm64 patch to no avail.

It very much *does* help.  Try harder?  Maybe you typoed?


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

On Wed, Aug 28, 2024 at 12:24:12PM +0000, Arnd Bergmann wrote:
> On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> >> > 
> >> > Is there a compiler flag that could be used to disable the generation of calls
> >> > to memset?
> >> 
> >> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> >> what it actually does (and how it avoids your problem, and mostly: learn
> >> what the actual problem *was*!)
> >
> > This might help with various loops, but it doesn't help with the matter
> > that this patch fixes, which is struct initialization. I just tried it
> > with the arm64 patch to no avail.
> 
> Maybe -ffreestanding can help here? That should cause the vdso to be built
> with the assumption that there is no libc, so it would neither add nor
> remove standard library calls. Not sure if that causes other problems,
> e.g. if the calling conventions are different.

"GCC requires the freestanding
environment provide 'memcpy', 'memmove', 'memset' and 'memcmp'."

This is precisely to implement things like struct initialisation.  Maybe
we should have a "-ffreeerstanding" or "-ffreefloating" or think of
something funnier still environment as well, this problem has been there
since the -ffreestanding flag has existed, but the problem is as old as
the night.

-fno-builtin might help a bit more, but just attack the problem at
its root, like I suggested?

(This isn't a new problem, originally it showed up as "GCC replaces
(part of) my memcpy() implementation by a (recursive) call to memcpy()"
and, well, that doesn't quite work!)


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Jason A. Donenfeld]

On Wed, Aug 28, 2024 at 07:33:13AM -0500, Segher Boessenkool wrote:
> On Wed, Aug 28, 2024 at 01:18:34PM +0200, Jason A. Donenfeld wrote:
> > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> > > On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > > > > +		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
> > > > > +			params->reserved[i] = 0;
> 
> This is a loop.  With -ftree-loop-distribute-patterns, the default at
> -O2, this is optimised to
> 
>     memset(params->reserved, 0, ...);
> 
> (which is perfectly fine, since memset is required to be there even
> for freestanding environments, this is documented!)
> 
> > > -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> > > what it actually does (and how it avoids your problem, and mostly: learn
> > > what the actual problem *was*!)
> > 
> > This might help with various loops, but it doesn't help with the matter
> > that this patch fixes, which is struct initialization. I just tried it
> > with the arm64 patch to no avail.
> 
> It very much *does* help.  Try harder?  Maybe you typoed?

Scroll up and reread the original patch. You are confused. The loop is
what fixes the matter. It's struct initialization that generates the
memset.

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

On Wed, Aug 28, 2024 at 02:26:08PM +0200, Jason A. Donenfeld wrote:
> On Wed, Aug 28, 2024 at 2:24 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> > >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > >> >
> > >> > Is there a compiler flag that could be used to disable the generation of calls
> > >> > to memset?
> > >>
> > >> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> > >> what it actually does (and how it avoids your problem, and mostly: learn
> > >> what the actual problem *was*!)
> > >
> > > This might help with various loops, but it doesn't help with the matter
> > > that this patch fixes, which is struct initialization. I just tried it
> > > with the arm64 patch to no avail.
> >
> > Maybe -ffreestanding can help here? That should cause the vdso to be built
> > with the assumption that there is no libc, so it would neither add nor
> > remove standard library calls. Not sure if that causes other problems,
> > e.g. if the calling conventions are different.
> 
> >From https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90701:
> 
> | You need -ffreestanding but that is documented to emit memset and
> memcpy still.

Yeah.

'-nostdlib'
     Do not use the standard system startup files or libraries when
     linking.

This won't help a bit, the compiler will still optimise your
initialisation loop to a memset() call, it just won't link to libgcc.a
and crt*.o and its ilk (which is not where mem* are implemented in the
first place!)


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Ard Biesheuvel]

On Wed, 28 Aug 2024 at 14:57, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> On Wed, Aug 28, 2024 at 12:24:12PM +0000, Arnd Bergmann wrote:
> > On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> > >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > >> >
> > >> > Is there a compiler flag that could be used to disable the generation of calls
> > >> > to memset?
> > >>
> > >> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> > >> what it actually does (and how it avoids your problem, and mostly: learn
> > >> what the actual problem *was*!)
> > >
> > > This might help with various loops, but it doesn't help with the matter
> > > that this patch fixes, which is struct initialization. I just tried it
> > > with the arm64 patch to no avail.
> >
> > Maybe -ffreestanding can help here? That should cause the vdso to be built
> > with the assumption that there is no libc, so it would neither add nor
> > remove standard library calls. Not sure if that causes other problems,
> > e.g. if the calling conventions are different.
>
> "GCC requires the freestanding
> environment provide 'memcpy', 'memmove', 'memset' and 'memcmp'."
>
> This is precisely to implement things like struct initialisation.  Maybe
> we should have a "-ffreeerstanding" or "-ffreefloating" or think of
> something funnier still environment as well, this problem has been there
> since the -ffreestanding flag has existed, but the problem is as old as
> the night.
>
> -fno-builtin might help a bit more, but just attack the problem at
> its root, like I suggested?
>

In my experience, this is likely to do the opposite: it causes the
compiler to 'forget' the semantics of memcpy() and memset(), so that
explicit trivial calls will no longer be elided and replaced with
plain loads and stores (as it can no longer guarantee the equivalence)

> (This isn't a new problem, originally it showed up as "GCC replaces
> (part of) my memcpy() implementation by a (recursive) call to memcpy()"
> and, well, that doesn't quite work!)
>

This needs to be fixed for Clang as well, so throwing GCC specific
flags at it will at best be a partial solution.

Omitting the struct assignment is a reasonable way to reduce the
likelihood that a memset() will be emitted, so for this patch

Acked-by: Ard Biesheuvel <ardb@kernel.org>

It is not a complete solution, unfortunately, and I guess there may be
other situations (compiler/arch combinations) where this might pop up
again.

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

Hi!

On Wed, Aug 28, 2024 at 05:40:23PM +0200, Ard Biesheuvel wrote:
> On Wed, 28 Aug 2024 at 14:57, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> >
> > On Wed, Aug 28, 2024 at 12:24:12PM +0000, Arnd Bergmann wrote:
> > > On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > > > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> > > >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > > >> >
> > > >> > Is there a compiler flag that could be used to disable the generation of calls
> > > >> > to memset?
> > > >>
> > > >> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> > > >> what it actually does (and how it avoids your problem, and mostly: learn
> > > >> what the actual problem *was*!)
> > > >
> > > > This might help with various loops, but it doesn't help with the matter
> > > > that this patch fixes, which is struct initialization. I just tried it
> > > > with the arm64 patch to no avail.
> > >
> > > Maybe -ffreestanding can help here? That should cause the vdso to be built
> > > with the assumption that there is no libc, so it would neither add nor
> > > remove standard library calls. Not sure if that causes other problems,
> > > e.g. if the calling conventions are different.
> >
> > "GCC requires the freestanding
> > environment provide 'memcpy', 'memmove', 'memset' and 'memcmp'."
> >
> > This is precisely to implement things like struct initialisation.  Maybe
> > we should have a "-ffreeerstanding" or "-ffreefloating" or think of
> > something funnier still environment as well, this problem has been there
> > since the -ffreestanding flag has existed, but the problem is as old as
> > the night.
> >
> > -fno-builtin might help a bit more, but just attack the problem at
> > its root, like I suggested?
> >
> 
> In my experience, this is likely to do the opposite: it causes the
> compiler to 'forget' the semantics of memcpy() and memset(), so that
> explicit trivial calls will no longer be elided and replaced with
> plain loads and stores (as it can no longer guarantee the equivalence)

No, the compiler will never forget those semantics.  But if you tell it
your function named memset() is not the actual standard memset -- via
-fno-builtin-memset for example -- the compiler won't optimise things
involving it quite as much.  You told it so eh?

You can also tell it not to have a __builtin_memset function, but in
this particular case that won;t quite work, since the compiler does need
to have that builtin available to do struct and array initialisations
and the like.

> > (This isn't a new problem, originally it showed up as "GCC replaces
> > (part of) my memcpy() implementation by a (recursive) call to memcpy()"
> > and, well, that doesn't quite work!)
> >
> 
> This needs to be fixed for Clang as well, so throwing GCC specific
> flags at it will at best be a partial solution.

clang says it is a 100% plug-in replacement for GCC, so they will have
to accept all GCC flags.  And in many cases they do.  Cases where they
don't are bugs.

> It is not a complete solution, unfortunately, and I guess there may be
> other situations (compiler/arch combinations) where this might pop up
> again.

Why do mem* not work in VDSOs?  Fix that, and all these problems
disappear, and you do not need workrarounds :-)


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Ard Biesheuvel]

On Wed, 28 Aug 2024 at 18:24, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> Hi!
>
> On Wed, Aug 28, 2024 at 05:40:23PM +0200, Ard Biesheuvel wrote:
> > On Wed, 28 Aug 2024 at 14:57, Segher Boessenkool
> > <segher@kernel.crashing.org> wrote:
> > >
> > > On Wed, Aug 28, 2024 at 12:24:12PM +0000, Arnd Bergmann wrote:
> > > > On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > > > > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> > > > >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> > > > >> >
> > > > >> > Is there a compiler flag that could be used to disable the generation of calls
> > > > >> > to memset?
> > > > >>
> > > > >> -fno-tree-loop-distribute-patterns .  But, as always, read up on it, see
> > > > >> what it actually does (and how it avoids your problem, and mostly: learn
> > > > >> what the actual problem *was*!)
> > > > >
> > > > > This might help with various loops, but it doesn't help with the matter
> > > > > that this patch fixes, which is struct initialization. I just tried it
> > > > > with the arm64 patch to no avail.
> > > >
> > > > Maybe -ffreestanding can help here? That should cause the vdso to be built
> > > > with the assumption that there is no libc, so it would neither add nor
> > > > remove standard library calls. Not sure if that causes other problems,
> > > > e.g. if the calling conventions are different.
> > >
> > > "GCC requires the freestanding
> > > environment provide 'memcpy', 'memmove', 'memset' and 'memcmp'."
> > >
> > > This is precisely to implement things like struct initialisation.  Maybe
> > > we should have a "-ffreeerstanding" or "-ffreefloating" or think of
> > > something funnier still environment as well, this problem has been there
> > > since the -ffreestanding flag has existed, but the problem is as old as
> > > the night.
> > >
> > > -fno-builtin might help a bit more, but just attack the problem at
> > > its root, like I suggested?
> > >
> >
> > In my experience, this is likely to do the opposite: it causes the
> > compiler to 'forget' the semantics of memcpy() and memset(), so that
> > explicit trivial calls will no longer be elided and replaced with
> > plain loads and stores (as it can no longer guarantee the equivalence)
>
> No, the compiler will never forget those semantics.  But if you tell it
> your function named memset() is not the actual standard memset -- via
> -fno-builtin-memset for example -- the compiler won't optimise things
> involving it quite as much.  You told it so eh?
>

That is exactly the point I am making. So how would this help in this case?

> You can also tell it not to have a __builtin_memset function, but in
> this particular case that won;t quite work, since the compiler does need
> to have that builtin available to do struct and array initialisations
> and the like.
>
> > > (This isn't a new problem, originally it showed up as "GCC replaces
> > > (part of) my memcpy() implementation by a (recursive) call to memcpy()"
> > > and, well, that doesn't quite work!)
> > >
> >
> > This needs to be fixed for Clang as well, so throwing GCC specific
> > flags at it will at best be a partial solution.
>
> clang says it is a 100% plug-in replacement for GCC, so they will have
> to accept all GCC flags.  And in many cases they do.  Cases where they
> don't are bugs.
>

Even if this were true, we support Clang versions today that do not
support -fno-tree-loop-distribute-patterns so my point stands.

> > It is not a complete solution, unfortunately, and I guess there may be
> > other situations (compiler/arch combinations) where this might pop up
> > again.
>
> Why do mem* not work in VDSOs?  Fix that, and all these problems
> disappear, and you do not need workrarounds :-)
>

Good point. We should just import memcpy and memset in the VDSO ELF metadata.

Not sure about static binaries, though: do those even use the VDSO?

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

On Wed, Aug 28, 2024 at 07:12:55PM +0200, Ard Biesheuvel wrote:
> On Wed, 28 Aug 2024 at 18:24, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> > > In my experience, this is likely to do the opposite: it causes the
> > > compiler to 'forget' the semantics of memcpy() and memset(), so that
> > > explicit trivial calls will no longer be elided and replaced with
> > > plain loads and stores (as it can no longer guarantee the equivalence)
> >
> > No, the compiler will never forget those semantics.  But if you tell it
> > your function named memset() is not the actual standard memset -- via
> > -fno-builtin-memset for example -- the compiler won't optimise things
> > involving it quite as much.  You told it so eh?
> 
> That is exactly the point I am making. So how would this help in this case?

I think we agree?  :-)

> > > This needs to be fixed for Clang as well, so throwing GCC specific
> > > flags at it will at best be a partial solution.
> >
> > clang says it is a 100% plug-in replacement for GCC, so they will have
> > to accept all GCC flags.  And in many cases they do.  Cases where they
> > don't are bugs.
> 
> Even if this were true, we support Clang versions today that do not
> support -fno-tree-loop-distribute-patterns so my point stands.

It is true.  Yes, this cause problems for their users.

> > > It is not a complete solution, unfortunately, and I guess there may be
> > > other situations (compiler/arch combinations) where this might pop up
> > > again.
> >
> > Why do mem* not work in VDSOs?  Fix that, and all these problems
> > disappear, and you do not need workrarounds :-)
> 
> Good point. We should just import memcpy and memset in the VDSO ELF metadata.

Yeah.  In many cases GCC will replace such calls by (faster and/or
smaller) inline code anyway, but when it does leave a call, there needs
to be an external function implementing it :-)

> Not sure about static binaries, though: do those even use the VDSO?

With "static binary" people usually mean "a binary not using any DSOs",
I think the VDSO is a DSO, also in this respect?  As always, -static
builds are *way* less problematic (and faster and smaller :-) )


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Christophe Leroy]

Le 28/08/2024 à 19:25, Segher Boessenkool a écrit :
> 
>> Not sure about static binaries, though: do those even use the VDSO?
> 
> With "static binary" people usually mean "a binary not using any DSOs",
> I think the VDSO is a DSO, also in this respect?  As always, -static
> builds are *way* less problematic (and faster and smaller :-) )
> 

AFAIK on powerpc even static binaries use the vDSO, otherwise signals 
don't work.

Christophe

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Segher Boessenkool]

On Thu, Aug 29, 2024 at 07:36:38PM +0200, Christophe Leroy wrote:
> 
> 
> Le 28/08/2024 à 19:25, Segher Boessenkool a écrit :
> >
> >>Not sure about static binaries, though: do those even use the VDSO?
> >
> >With "static binary" people usually mean "a binary not using any DSOs",
> >I think the VDSO is a DSO, also in this respect?  As always, -static
> >builds are *way* less problematic (and faster and smaller :-) )
> >
> 
> AFAIK on powerpc even static binaries use the vDSO, otherwise signals 
> don't work.

How can that work?  Non-dynamic binaries do not use ld.so (that is the
definition of a dynamic binary, even).  So they cannot link (at runtime)
to any DSO (unless that is done manually?!)

Maybe there is something at a fixed offset in the vDSO, or something
like that?  Is this documented somewhere?


Segher

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Christophe Leroy]

Le 29/08/2024 à 20:02, Segher Boessenkool a écrit :
> On Thu, Aug 29, 2024 at 07:36:38PM +0200, Christophe Leroy wrote:
>>
>>
>> Le 28/08/2024 à 19:25, Segher Boessenkool a écrit :
>>>
>>>> Not sure about static binaries, though: do those even use the VDSO?
>>>
>>> With "static binary" people usually mean "a binary not using any DSOs",
>>> I think the VDSO is a DSO, also in this respect?  As always, -static
>>> builds are *way* less problematic (and faster and smaller :-) )
>>>
>>
>> AFAIK on powerpc even static binaries use the vDSO, otherwise signals
>> don't work.
> 
> How can that work?  Non-dynamic binaries do not use ld.so (that is the
> definition of a dynamic binary, even).  So they cannot link (at runtime)
> to any DSO (unless that is done manually?!)
> 
> Maybe there is something at a fixed offset in the vDSO, or something
> like that?  Is this documented somewhere?
> 

You've got some explanation here : 
https://github.com/torvalds/linux/blob/master/Documentation/ABI/stable/vdso

Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

[Michael Ellerman]

Segher Boessenkool <segher@kernel.crashing.org> writes:
> On Thu, Aug 29, 2024 at 07:36:38PM +0200, Christophe Leroy wrote:
>> 
>> 
>> Le 28/08/2024 à 19:25, Segher Boessenkool a écrit :
>> >
>> >>Not sure about static binaries, though: do those even use the VDSO?
>> >
>> >With "static binary" people usually mean "a binary not using any DSOs",
>> >I think the VDSO is a DSO, also in this respect?  As always, -static
>> >builds are *way* less problematic (and faster and smaller :-) )
>> >
>> 
>> AFAIK on powerpc even static binaries use the vDSO, otherwise signals 
>> don't work.
>
> How can that work?  Non-dynamic binaries do not use ld.so (that is the
> definition of a dynamic binary, even).  So they cannot link (at runtime)
> to any DSO (unless that is done manually?!)

At least for signals I don't think the application needs to know
anything about the VDSO. The kernel sets up the return to the signal
trampoline (in the VDSO), and as long as userspace returns from its
signal handler with blr it will land back on the trampoline.

cheers