[PATCH v7 0/5] x86/pkeys: update PKRU to enable pkey 0 before

[PATCH v7 0/5] x86/pkeys: update PKRU to enable pkey 0 before

[Aruna Ramakrishna]

v7 updates:
- Rebased patchset to v6.11.0-rc1
- Removed ia32 and x32 function interface changes as PKRU is only
  supported in 64-bit mode, as suggested by Jeff Xu

v6 updates:
- Rebased patchset to v6.10.0-rc5
- Changed sig_prepare_pkru() back to enabling all pkeys, based on
  discussion with Jeff Xu

v5 updates:
- No major changes, mostly a resend of v4 - except for updating the
  commit description for patch 5/5

v4 updates (based on review feedback from Thomas Gleixner):
- Simplified update_pkru_in_sigframe()
- Changed sigpkru to enable minimally required keys (init_pkru and
  current
  pkru)
- Modified pkey_sighandler_tests.c to use kselfttest framework
- Fixed commit descriptions
- Fixed sigreturn use case (pointed out by Jeff Xu)
- Added a new sigreturn test case

v3 updates (based on review feedback from Ingo Molnar and Dave Hansen):
- Split the original patch into 3:
        - function interface changes
        - helper functions
        - functional change to write pkru on sigframe
- Enabled all pkeys before XSAVE - i.e. wrpkru(0), rather than assuming
that the alt sig stack is always protected by pkey 0.
- Added a few test cases in pkey_sighandler_tests.c.

I had some trouble adding these tests to
tools/testing/selftests/mm/protection_keys.c, so they're in a separate
file.

Aruna Ramakrishna (4):
  x86/pkeys: Add PKRU as a parameter in signal handling functions
  x86/pkeys: Add helper functions to update PKRU on the sigframe
  x86/pkeys: Update PKRU to enable all pkeys before XSAVE
  x86/pkeys: Restore altstack before sigcontext

Keith Lucas (1):
  selftests/mm: Add new testcases for pkeys

 arch/x86/include/asm/fpu/signal.h             |   2 +-
 arch/x86/kernel/fpu/signal.c                  |  27 +-
 arch/x86/kernel/fpu/xstate.c                  |  13 +
 arch/x86/kernel/fpu/xstate.h                  |   2 +
 arch/x86/kernel/signal.c                      |  29 +-
 arch/x86/kernel/signal_64.c                   |   6 +-
 tools/testing/selftests/mm/Makefile           |   2 +
 tools/testing/selftests/mm/pkey-helpers.h     |  11 +-
 .../selftests/mm/pkey_sighandler_tests.c      | 479 ++++++++++++++++++
 tools/testing/selftests/mm/protection_keys.c  |  10 -
 10 files changed, 560 insertions(+), 21 deletions(-)
 create mode 100644 tools/testing/selftests/mm/pkey_sighandler_tests.c


base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b
prerequisite-patch-id: 7b2144970da943b19b53baab525a0fc653fcd7b8
-- 
2.39.3

[PATCH v7 1/5] x86/pkeys: Add PKRU as a parameter in signal handling functions

[Aruna Ramakrishna]

Problem description:
Let's assume there's a multithreaded application that runs untrusted
user code. Each thread has its stack/code protected by a non-zero pkey,
and the PKRU register is set up such that only that particular non-zero
pkey is enabled. Each thread also sets up an alternate signal stack to
handle signals, which is protected by pkey zero. The pkeys man page
documents that the PKRU will be reset to init_pkru when the signal
handler is invoked, which means that pkey zero access will be enabled.
But this reset happens after the kernel attempts to push fpu state
to the alternate stack, which is not (yet) accessible by the kernel,
which leads to a new SIGSEGV being sent to the application, terminating
it.

Enabling both the non-zero pkey (for the thread) and pkey zero in
userspace will not work for this use case. We cannot have the alt stack
writeable by all - the rationale here is that the code running in that
thread (using a non-zero pkey) is untrusted and should not have access
to the alternate signal stack (that uses pkey zero), to prevent the
return address of a function from being changed. The expectation is that
kernel should be able to set up the alternate signal stack and deliver
the signal to the application even if pkey zero is explicitly disabled
by the application. The signal handler accessibility should not be
dictated by whatever PKRU value the thread sets up.

Solution:
The PKRU register is managed by XSAVE, which means the sigframe contents
must match the register contents - which is not the case here. We want
the sigframe to contain the user-defined PKRU value (so that it is
restored correctly from sigcontext) but the actual register must be
reset to init_pkru so that the alt stack is accessible and the signal
can be delivered to the application. It seems that the proper fix here
would be to remove PKRU from the XSAVE framework and manage it
separately, which is quite complicated. As a workaround, do this:

        orig_pkru = rdpkru();
        wrpkru(orig_pkru & init_pkru_value);
        xsave_to_user_sigframe();
        put_user(pkru_sigframe_addr, orig_pkru)

This change is split over multiple patches.

In preparation for writing PKRU to sigframe in a later patch, pass in
PKRU as an additional parameter down the chain from get_sigframe():
	get_sigframe()
          copy_fpstate_to_sigframe()
            copy_fpregs_to_sigframe()

There are no functional changes in this patch.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
---
 arch/x86/include/asm/fpu/signal.h | 2 +-
 arch/x86/kernel/fpu/signal.c      | 6 +++---
 arch/x86/kernel/signal.c          | 3 ++-
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/fpu/signal.h b/arch/x86/include/asm/fpu/signal.h
index 611fa41711af..eccc75bc9c4f 100644
--- a/arch/x86/include/asm/fpu/signal.h
+++ b/arch/x86/include/asm/fpu/signal.h
@@ -29,7 +29,7 @@ fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 
 unsigned long fpu__get_fpstate_size(void);
 
-extern bool copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size);
+extern bool copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size, u32 pkru);
 extern void fpu__clear_user_states(struct fpu *fpu);
 extern bool fpu__restore_sig(void __user *buf, int ia32_frame);
 
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 247f2225aa9f..2b3b9e140dd4 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -156,7 +156,7 @@ static inline bool save_xstate_epilog(void __user *buf, int ia32_frame,
 	return !err;
 }
 
-static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
+static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pkru)
 {
 	if (use_xsave())
 		return xsave_to_user_sigframe(buf);
@@ -185,7 +185,7 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
  * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
  * indicating the absence/presence of the extended state to the user.
  */
-bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
+bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size, u32 pkru)
 {
 	struct task_struct *tsk = current;
 	struct fpstate *fpstate = tsk->thread.fpu.fpstate;
@@ -228,7 +228,7 @@ bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 		fpregs_restore_userregs();
 
 	pagefault_disable();
-	ret = copy_fpregs_to_sigframe(buf_fx);
+	ret = copy_fpregs_to_sigframe(buf_fx, pkru);
 	pagefault_enable();
 	fpregs_unlock();
 
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 31b6f5dddfc2..1f1e8e0ac5a3 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -84,6 +84,7 @@ get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
 	unsigned long math_size = 0;
 	unsigned long sp = regs->sp;
 	unsigned long buf_fx = 0;
+	u32 pkru = read_pkru();
 
 	/* redzone */
 	if (!ia32_frame)
@@ -139,7 +140,7 @@ get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
 	}
 
 	/* save i387 and extended state */
-	if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size))
+	if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size, pkru))
 		return (void __user *)-1L;
 
 	return (void __user *)sp;
-- 
2.39.3

[PATCH v7 2/5] x86/pkeys: Add helper functions to update PKRU on the sigframe

[Aruna Ramakrishna]

In the case where a user thread sets up an alternate signal stack
protected by the default pkey (i.e. pkey 0), while the thread's stack
is protected by a non-zero pkey, both these pkeys have to be enabled in
the PKRU register for the signal to be delivered to the application
correctly. However, the PKRU value restored after handling the signal
must not enable this extra pkey (i.e. pkey 0), so the PKRU value on the
on the sigframe should be overwritten with the user-defined value.

Add helper functions that will update PKRU value on the sigframe after
XSAVE. These functions will be called in a later patch; this patch does
not change any behavior as yet.

Note that sig_prepare_pkru() makes no assumption about what pkey could
be used to protect the altstack (i.e. it may not be part of init_pkru),
and so enables all pkeys.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
---
 arch/x86/kernel/fpu/signal.c | 10 ++++++++++
 arch/x86/kernel/fpu/xstate.c | 13 +++++++++++++
 arch/x86/kernel/fpu/xstate.h |  2 ++
 arch/x86/kernel/signal.c     | 18 ++++++++++++++++++
 4 files changed, 43 insertions(+)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 2b3b9e140dd4..931c5469d7f3 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -63,6 +63,16 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
 	return true;
 }
 
+/*
+ * Update the value of PKRU register that was already pushed onto the signal frame.
+ */
+static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u32 pkru)
+{
+	if (unlikely(!cpu_feature_enabled(X86_FEATURE_OSPKE)))
+		return 0;
+	return __put_user(pkru, (unsigned int __user *)get_xsave_addr_user(buf, XFEATURE_PKRU));
+}
+
 /*
  * Signal frame handlers.
  */
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index c5a026fee5e0..fa7628bb541b 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -993,6 +993,19 @@ void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr)
 }
 EXPORT_SYMBOL_GPL(get_xsave_addr);
 
+/*
+ * Given an xstate feature nr, calculate where in the xsave buffer the state is.
+ * The xsave buffer should be in standard format, not compacted (e.g. user mode
+ * signal frames).
+ */
+void __user *get_xsave_addr_user(struct xregs_state __user *xsave, int xfeature_nr)
+{
+	if (WARN_ON_ONCE(!xfeature_enabled(xfeature_nr)))
+		return NULL;
+
+	return (void __user *)xsave + xstate_offsets[xfeature_nr];
+}
+
 #ifdef CONFIG_ARCH_HAS_PKEYS
 
 /*
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 2ee0b9c53dcc..d04383793676 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -54,6 +54,8 @@ extern int copy_sigframe_from_user_to_xstate(struct task_struct *tsk, const void
 extern void fpu__init_cpu_xstate(void);
 extern void fpu__init_system_xstate(unsigned int legacy_size);
 
+extern void __user *get_xsave_addr_user(struct xregs_state *xsave, int xfeature_nr);
+
 static inline u64 xfeatures_mask_supervisor(void)
 {
 	return fpu_kernel_cfg.max_features & XFEATURE_MASK_SUPERVISOR_SUPPORTED;
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 1f1e8e0ac5a3..9dc77ad03a0e 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -60,6 +60,24 @@ static inline int is_x32_frame(struct ksignal *ksig)
 		ksig->ka.sa.sa_flags & SA_X32_ABI;
 }
 
+/*
+ * Enable all pkeys temporarily, so as to ensure that both the current
+ * execution stack as well as the alternate signal stack are writeable.
+ * The application can use any of the available pkeys to protect the
+ * alternate signal stack, and we don't know which one it is, so enable
+ * all. The PKRU register will be reset to init_pkru later in the flow,
+ * in fpu__clear_user_states(), and it is the application's responsibility
+ * to enable the appropriate pkey as the first step in the signal handler
+ * so that the handler does not segfault.
+ */
+static inline u32 sig_prepare_pkru(void)
+{
+	u32 orig_pkru = read_pkru();
+
+	write_pkru(0);
+	return orig_pkru;
+}
+
 /*
  * Set up a signal frame.
  */
-- 
2.39.3

[PATCH v7 3/5] x86/pkeys: Update PKRU to enable all pkeys before XSAVE

[Aruna Ramakrishna]

If the alternate signal stack is protected by a different pkey than the
current execution stack, copying xsave data to the sigaltstack will fail
if its pkey is not enabled. We do not know which pkey was used by the
application for the sigaltstack, so enable all pkeys before xsave
so that the signal handler accessibility is not dictated by the PKRU
value that the thread sets up. But this updated PKRU value is also
pushed onto the sigframe, so overwrite that with the original,
user-defined PKRU value so that the value restored from sigcontext does
not have the extra pkey enabled.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
---
 arch/x86/kernel/fpu/signal.c | 11 +++++++++--
 arch/x86/kernel/signal.c     | 12 ++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 931c5469d7f3..1065ab995305 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -168,8 +168,15 @@ static inline bool save_xstate_epilog(void __user *buf, int ia32_frame,
 
 static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pkru)
 {
-	if (use_xsave())
-		return xsave_to_user_sigframe(buf);
+	int err = 0;
+
+	if (use_xsave()) {
+		err = xsave_to_user_sigframe(buf);
+		if (!err)
+			err = update_pkru_in_sigframe(buf, pkru);
+		return err;
+	}
+
 	if (use_fxsr())
 		return fxsave_to_user_sigframe((struct fxregs_state __user *) buf);
 	else
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 9dc77ad03a0e..5f441039b572 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -102,7 +102,7 @@ get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
 	unsigned long math_size = 0;
 	unsigned long sp = regs->sp;
 	unsigned long buf_fx = 0;
-	u32 pkru = read_pkru();
+	u32 pkru;
 
 	/* redzone */
 	if (!ia32_frame)
@@ -157,9 +157,17 @@ get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
 		return (void __user *)-1L;
 	}
 
+	/* Update PKRU to enable access to the alternate signal stack. */
+	pkru = sig_prepare_pkru();
 	/* save i387 and extended state */
-	if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size, pkru))
+	if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size, pkru)) {
+		/*
+		 * Restore PKRU to the original, user-defined value; disable
+		 * extra pkeys enabled for the alternate signal stack, if any.
+		 */
+		write_pkru(pkru);
 		return (void __user *)-1L;
+	}
 
 	return (void __user *)sp;
 }
-- 
2.39.3

[PATCH v7 4/5] x86/pkeys: Restore altstack before sigcontext

[Aruna Ramakrishna]

A process can disable access to the alternate signal stack and still
expect signals to be delivered correctly. get_sigframe() updates the
PKRU value to enable access to the altstack, and makes sure that the
value on the sigframe is the user-defined PKRU value so that it is
correctly restored. However, in sigreturn(), restore_altstack() needs
read access to the altstack. But the PKRU has already been restored
from the sigframe (in restore_sigcontext()) which will disable access
to the altstack, resulting in a SIGSEGV.

Fix this by restoring altstack before restoring PKRU.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
---
 arch/x86/kernel/signal_64.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index 8a94053c5444..ee9453891901 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -260,13 +260,13 @@ SYSCALL_DEFINE0(rt_sigreturn)
 
 	set_current_blocked(&set);
 
-	if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
+	if (restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-	if (restore_signal_shadow_stack())
+	if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
 		goto badframe;
 
-	if (restore_altstack(&frame->uc.uc_stack))
+	if (restore_signal_shadow_stack())
 		goto badframe;
 
 	return regs->ax;
-- 
2.39.3

[PATCH v7 5/5] selftests/mm: Add new testcases for pkeys

[Aruna Ramakrishna]

From: Keith Lucas <keith.lucas@oracle.com>

Add a few new tests to exercise the signal handler flow,
especially with pkey 0 disabled.

There are 5 new tests added:
- test_sigsegv_handler_with_pkey0_disabled
- test_sigsegv_handler_cannot_access_stack
- test_sigsegv_handler_with_different_pkey_for_stack
- test_pkru_preserved_after_sigusr1
- test_pkru_sigreturn

[ Aruna: Adapted to upstream ]

Signed-off-by: Keith Lucas <keith.lucas@oracle.com>
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
---
 tools/testing/selftests/mm/Makefile           |   2 +
 tools/testing/selftests/mm/pkey-helpers.h     |  11 +-
 .../selftests/mm/pkey_sighandler_tests.c      | 479 ++++++++++++++++++
 tools/testing/selftests/mm/protection_keys.c  |  10 -
 4 files changed, 491 insertions(+), 11 deletions(-)
 create mode 100644 tools/testing/selftests/mm/pkey_sighandler_tests.c

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 901e0d07765b..0123a3a0bb17 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -88,6 +88,7 @@ CAN_BUILD_X86_64 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_64bit_pr
 CAN_BUILD_WITH_NOPIE := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_program.c -no-pie)
 
 VMTARGETS := protection_keys
+VMTARGETS := pkey_sighandler_tests
 BINARIES_32 := $(VMTARGETS:%=%_32)
 BINARIES_64 := $(VMTARGETS:%=%_64)
 
@@ -106,6 +107,7 @@ else
 
 ifneq (,$(findstring $(ARCH),powerpc))
 TEST_GEN_FILES += protection_keys
+TEST_GEN_FILES += pkey_sighandler_tests
 endif
 
 endif
diff --git a/tools/testing/selftests/mm/pkey-helpers.h b/tools/testing/selftests/mm/pkey-helpers.h
index 1af3156a9db8..2b1189c27167 100644
--- a/tools/testing/selftests/mm/pkey-helpers.h
+++ b/tools/testing/selftests/mm/pkey-helpers.h
@@ -12,6 +12,7 @@
 #include <stdlib.h>
 #include <ucontext.h>
 #include <sys/mman.h>
+#include <linux/compiler.h>
 
 #include "../kselftest.h"
 
@@ -79,7 +80,15 @@ extern void abort_hooks(void);
 	}					\
 } while (0)
 
-__attribute__((noinline)) int read_ptr(int *ptr);
+noinline int read_ptr(int *ptr)
+{
+	/*
+	 * Keep GCC from optimizing this away somehow
+	 */
+	barrier();
+	return *ptr;
+}
+
 void expected_pkey_fault(int pkey);
 int sys_pkey_alloc(unsigned long flags, unsigned long init_val);
 int sys_pkey_free(unsigned long pkey);
diff --git a/tools/testing/selftests/mm/pkey_sighandler_tests.c b/tools/testing/selftests/mm/pkey_sighandler_tests.c
new file mode 100644
index 000000000000..c43030c7056d
--- /dev/null
+++ b/tools/testing/selftests/mm/pkey_sighandler_tests.c
@@ -0,0 +1,479 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Tests Memory Protection Keys (see Documentation/core-api/protection-keys.rst)
+ *
+ * The testcases in this file exercise various flows related to signal handling,
+ * using an alternate signal stack, with the default pkey (pkey 0) disabled.
+ *
+ * Compile with:
+ * gcc -mxsave      -o pkey_sighandler_tests -O2 -g -std=gnu99 -pthread -Wall pkey_sighandler_tests.c -I../../../../tools/include -lrt -ldl -lm
+ * gcc -mxsave -m32 -o pkey_sighandler_tests -O2 -g -std=gnu99 -pthread -Wall pkey_sighandler_tests.c -I../../../../tools/include -lrt -ldl -lm
+ */
+#define _GNU_SOURCE
+#define __SANE_USERSPACE_TYPES__
+#include <errno.h>
+#include <sys/syscall.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <signal.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <limits.h>
+
+#include "pkey-helpers.h"
+
+#define STACK_SIZE PTHREAD_STACK_MIN
+
+void expected_pkey_fault(int pkey) {}
+
+pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
+siginfo_t siginfo = {0};
+
+/*
+ * We need to use inline assembly instead of glibc's syscall because glibc's
+ * syscall will attempt to access the PLT in order to call a library function
+ * which is protected by MPK 0 which we don't have access to.
+ */
+static inline __always_inline
+long syscall_raw(long n, long a1, long a2, long a3, long a4, long a5, long a6)
+{
+	unsigned long ret;
+#ifdef __x86_64__
+	register long r10 asm("r10") = a4;
+	register long r8 asm("r8") = a5;
+	register long r9 asm("r9") = a6;
+	asm volatile ("syscall"
+		      : "=a"(ret)
+		      : "a"(n), "D"(a1), "S"(a2), "d"(a3), "r"(r10), "r"(r8), "r"(r9)
+		      : "rcx", "r11", "memory");
+#elif defined __i386__
+	asm volatile ("int $0x80"
+		      : "=a"(ret)
+		      : "a"(n), "b"(a1), "c"(a2), "d"(a3), "S"(a4), "D"(a5)
+		      : "memory");
+#endif
+	return ret;
+}
+
+static void sigsegv_handler(int signo, siginfo_t *info, void *ucontext)
+{
+	pthread_mutex_lock(&mutex);
+
+	memcpy(&siginfo, info, sizeof(siginfo_t));
+
+	pthread_cond_signal(&cond);
+	pthread_mutex_unlock(&mutex);
+
+	syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
+}
+
+static void sigusr1_handler(int signo, siginfo_t *info, void *ucontext)
+{
+	pthread_mutex_lock(&mutex);
+
+	memcpy(&siginfo, info, sizeof(siginfo_t));
+
+	pthread_cond_signal(&cond);
+	pthread_mutex_unlock(&mutex);
+}
+
+static void sigusr2_handler(int signo, siginfo_t *info, void *ucontext)
+{
+	/*
+	 * pkru should be the init_pkru value which enabled MPK 0 so
+	 * we can use library functions.
+	 */
+	printf("%s invoked.\n", __func__);
+}
+
+static void raise_sigusr2(void)
+{
+	pid_t tid = 0;
+
+	tid = syscall_raw(SYS_gettid, 0, 0, 0, 0, 0, 0);
+
+	syscall_raw(SYS_tkill, tid, SIGUSR2, 0, 0, 0, 0);
+
+	/*
+	 * We should return from the signal handler here and be able to
+	 * return to the interrupted thread.
+	 */
+}
+
+static void *thread_segv_with_pkey0_disabled(void *ptr)
+{
+	/* Disable MPK 0 (and all others too) */
+	__write_pkey_reg(0x55555555);
+
+	/* Segfault (with SEGV_MAPERR) */
+	*(int *) (0x1) = 1;
+	return NULL;
+}
+
+static void *thread_segv_pkuerr_stack(void *ptr)
+{
+	/* Disable MPK 0 (and all others too) */
+	__write_pkey_reg(0x55555555);
+
+	/* After we disable MPK 0, we can't access the stack to return */
+	return NULL;
+}
+
+static void *thread_segv_maperr_ptr(void *ptr)
+{
+	stack_t *stack = ptr;
+	int *bad = (int *)1;
+
+	/*
+	 * Setup alternate signal stack, which should be pkey_mprotect()ed by
+	 * MPK 0. The thread's stack cannot be used for signals because it is
+	 * not accessible by the default init_pkru value of 0x55555554.
+	 */
+	syscall_raw(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
+
+	/* Disable MPK 0.  Only MPK 1 is enabled. */
+	__write_pkey_reg(0x55555551);
+
+	/* Segfault */
+	*bad = 1;
+	syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
+	return NULL;
+}
+
+/*
+ * Verify that the sigsegv handler is invoked when pkey 0 is disabled.
+ * Note that the new thread stack and the alternate signal stack is
+ * protected by MPK 0.
+ */
+static void test_sigsegv_handler_with_pkey0_disabled(void)
+{
+	struct sigaction sa;
+	pthread_attr_t attr;
+	pthread_t thr;
+
+	sa.sa_flags = SA_SIGINFO;
+
+	sa.sa_sigaction = sigsegv_handler;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(SIGSEGV, &sa, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	memset(&siginfo, 0, sizeof(siginfo));
+
+	pthread_attr_init(&attr);
+	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+
+	pthread_create(&thr, &attr, thread_segv_with_pkey0_disabled, NULL);
+
+	pthread_mutex_lock(&mutex);
+	while (siginfo.si_signo == 0)
+		pthread_cond_wait(&cond, &mutex);
+	pthread_mutex_unlock(&mutex);
+
+	ksft_test_result(siginfo.si_signo == SIGSEGV &&
+			 siginfo.si_code == SEGV_MAPERR &&
+			 siginfo.si_addr == (void *)1,
+			 "%s\n", __func__);
+}
+
+/*
+ * Verify that the sigsegv handler is invoked when pkey 0 is disabled.
+ * Note that the new thread stack and the alternate signal stack is
+ * protected by MPK 0, which renders them inaccessible when MPK 0
+ * is disabled. So just the return from the thread should cause a
+ * segfault with SEGV_PKUERR.
+ */
+static void test_sigsegv_handler_cannot_access_stack(void)
+{
+	struct sigaction sa;
+	pthread_attr_t attr;
+	pthread_t thr;
+
+	sa.sa_flags = SA_SIGINFO;
+
+	sa.sa_sigaction = sigsegv_handler;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(SIGSEGV, &sa, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	memset(&siginfo, 0, sizeof(siginfo));
+
+	pthread_attr_init(&attr);
+	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+
+	pthread_create(&thr, &attr, thread_segv_pkuerr_stack, NULL);
+
+	pthread_mutex_lock(&mutex);
+	while (siginfo.si_signo == 0)
+		pthread_cond_wait(&cond, &mutex);
+	pthread_mutex_unlock(&mutex);
+
+	ksft_test_result(siginfo.si_signo == SIGSEGV &&
+			 siginfo.si_code == SEGV_PKUERR,
+			 "%s\n", __func__);
+}
+
+/*
+ * Verify that the sigsegv handler that uses an alternate signal stack
+ * is correctly invoked for a thread which uses a non-zero MPK to protect
+ * its own stack, and disables all other MPKs (including 0).
+ */
+static void test_sigsegv_handler_with_different_pkey_for_stack(void)
+{
+	struct sigaction sa;
+	static stack_t sigstack;
+	void *stack;
+	int pkey;
+	int parent_pid = 0;
+	int child_pid = 0;
+
+	sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+
+	sa.sa_sigaction = sigsegv_handler;
+
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(SIGSEGV, &sa, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	stack = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE,
+		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+	assert(stack != MAP_FAILED);
+
+	/* Allow access to MPK 0 and MPK 1 */
+	__write_pkey_reg(0x55555550);
+
+	/* Protect the new stack with MPK 1 */
+	pkey = pkey_alloc(0, 0);
+	pkey_mprotect(stack, STACK_SIZE, PROT_READ | PROT_WRITE, pkey);
+
+	/* Set up alternate signal stack that will use the default MPK */
+	sigstack.ss_sp = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
+			      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	sigstack.ss_flags = 0;
+	sigstack.ss_size = STACK_SIZE;
+
+	memset(&siginfo, 0, sizeof(siginfo));
+
+	/* Use clone to avoid newer glibcs using rseq on new threads */
+	long ret = syscall_raw(SYS_clone,
+			       CLONE_VM | CLONE_FS | CLONE_FILES |
+			       CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
+			       CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
+			       CLONE_DETACHED,
+			       (long) ((char *)(stack) + STACK_SIZE),
+			       (long) &parent_pid,
+			       (long) &child_pid, 0, 0);
+
+	if (ret < 0) {
+		errno = -ret;
+		perror("clone");
+	} else if (ret == 0) {
+		thread_segv_maperr_ptr(&sigstack);
+		syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
+	}
+
+	pthread_mutex_lock(&mutex);
+	while (siginfo.si_signo == 0)
+		pthread_cond_wait(&cond, &mutex);
+	pthread_mutex_unlock(&mutex);
+
+	ksft_test_result(siginfo.si_signo == SIGSEGV &&
+			 siginfo.si_code == SEGV_MAPERR &&
+			 siginfo.si_addr == (void *)1,
+			 "%s\n", __func__);
+}
+
+/*
+ * Verify that the PKRU value set by the application is correctly
+ * restored upon return from signal handling.
+ */
+static void test_pkru_preserved_after_sigusr1(void)
+{
+	struct sigaction sa;
+	unsigned long pkru = 0x45454544;
+
+	sa.sa_flags = SA_SIGINFO;
+
+	sa.sa_sigaction = sigusr1_handler;
+	sigemptyset(&sa.sa_mask);
+	if (sigaction(SIGUSR1, &sa, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	memset(&siginfo, 0, sizeof(siginfo));
+
+	__write_pkey_reg(pkru);
+
+	raise(SIGUSR1);
+
+	pthread_mutex_lock(&mutex);
+	while (siginfo.si_signo == 0)
+		pthread_cond_wait(&cond, &mutex);
+	pthread_mutex_unlock(&mutex);
+
+	/* Ensure the pkru value is the same after returning from signal. */
+	ksft_test_result(pkru == __read_pkey_reg() &&
+			 siginfo.si_signo == SIGUSR1,
+			 "%s\n", __func__);
+}
+
+static noinline void *thread_sigusr2_self(void *ptr)
+{
+	/*
+	 * A const char array like "Resuming after SIGUSR2" won't be stored on
+	 * the stack and the code could access it via an offset from the program
+	 * counter. This makes sure it's on the function's stack frame.
+	 */
+	char str[] = {'R', 'e', 's', 'u', 'm', 'i', 'n', 'g', ' ',
+		'a', 'f', 't', 'e', 'r', ' ',
+		'S', 'I', 'G', 'U', 'S', 'R', '2',
+		'.', '.', '.', '\n', '\0'};
+	stack_t *stack = ptr;
+
+	/*
+	 * Setup alternate signal stack, which should be pkey_mprotect()ed by
+	 * MPK 0. The thread's stack cannot be used for signals because it is
+	 * not accessible by the default init_pkru value of 0x55555554.
+	 */
+	syscall(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
+
+	/* Disable MPK 0.  Only MPK 2 is enabled. */
+	__write_pkey_reg(0x55555545);
+
+	raise_sigusr2();
+
+	/* Do something, to show the thread resumed execution after the signal */
+	syscall_raw(SYS_write, 1, (long) str, sizeof(str) - 1, 0, 0, 0);
+
+	/*
+	 * We can't return to test_pkru_sigreturn because it
+	 * will attempt to use a %rbp value which is on the stack
+	 * of the main thread.
+	 */
+	syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
+	return NULL;
+}
+
+/*
+ * Verify that sigreturn is able to restore altstack even if the thread had
+ * disabled pkey 0.
+ */
+static void test_pkru_sigreturn(void)
+{
+	struct sigaction sa = {0};
+	static stack_t sigstack;
+	void *stack;
+	int pkey;
+	int parent_pid = 0;
+	int child_pid = 0;
+
+	sa.sa_handler = SIG_DFL;
+	sa.sa_flags = 0;
+	sigemptyset(&sa.sa_mask);
+
+	/*
+	 * For this testcase, we do not want to handle SIGSEGV. Reset handler
+	 * to default so that the application can crash if it receives SIGSEGV.
+	 */
+	if (sigaction(SIGSEGV, &sa, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+	sa.sa_sigaction = sigusr2_handler;
+	sigemptyset(&sa.sa_mask);
+
+	if (sigaction(SIGUSR2, &sa, NULL) == -1) {
+		perror("sigaction");
+		exit(EXIT_FAILURE);
+	}
+
+	stack = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE,
+		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+	assert(stack != MAP_FAILED);
+
+	/*
+	 * Allow access to MPK 0 and MPK 2. The child thread (to be created
+	 * later in this flow) will have its stack protected by MPK 2, whereas
+	 * the current thread's stack is protected by the default MPK 0. Hence
+	 * both need to be enabled.
+	 */
+	__write_pkey_reg(0x55555544);
+
+	/* Protect the stack with MPK 2 */
+	pkey = pkey_alloc(0, 0);
+	pkey_mprotect(stack, STACK_SIZE, PROT_READ | PROT_WRITE, pkey);
+
+	/* Set up alternate signal stack that will use the default MPK */
+	sigstack.ss_sp = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
+			      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	sigstack.ss_flags = 0;
+	sigstack.ss_size = STACK_SIZE;
+
+	/* Use clone to avoid newer glibcs using rseq on new threads */
+	long ret = syscall_raw(SYS_clone,
+			       CLONE_VM | CLONE_FS | CLONE_FILES |
+			       CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
+			       CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
+			       CLONE_DETACHED,
+			       (long) ((char *)(stack) + STACK_SIZE),
+			       (long) &parent_pid,
+			       (long) &child_pid, 0, 0);
+
+	if (ret < 0) {
+		errno = -ret;
+		perror("clone");
+	}  else if (ret == 0) {
+		thread_sigusr2_self(&sigstack);
+		syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
+	}
+
+	child_pid =  ret;
+	/* Check that thread exited */
+	do {
+		sched_yield();
+		ret = syscall_raw(SYS_tkill, child_pid, 0, 0, 0, 0, 0);
+	} while (ret != -ESRCH && ret != -EINVAL);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+void (*pkey_tests[])(void) = {
+	test_sigsegv_handler_with_pkey0_disabled,
+	test_sigsegv_handler_cannot_access_stack,
+	test_sigsegv_handler_with_different_pkey_for_stack,
+	test_pkru_preserved_after_sigusr1,
+	test_pkru_sigreturn
+};
+
+int main(int argc, char *argv[])
+{
+	int i;
+
+	ksft_print_header();
+	ksft_set_plan(ARRAY_SIZE(pkey_tests));
+
+	for (i = 0; i < ARRAY_SIZE(pkey_tests); i++)
+		(*pkey_tests[i])();
+
+	ksft_finished();
+	return 0;
+}
diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
index eaa6d1fc5328..cc6de1644360 100644
--- a/tools/testing/selftests/mm/protection_keys.c
+++ b/tools/testing/selftests/mm/protection_keys.c
@@ -950,16 +950,6 @@ void close_test_fds(void)
 	nr_test_fds = 0;
 }
 
-#define barrier() __asm__ __volatile__("": : :"memory")
-__attribute__((noinline)) int read_ptr(int *ptr)
-{
-	/*
-	 * Keep GCC from optimizing this away somehow
-	 */
-	barrier();
-	return *ptr;
-}
-
 void test_pkey_alloc_free_attach_pkey0(int *ptr, u16 pkey)
 {
 	int i, err;
-- 
2.39.3

Re: [PATCH v7 2/5] x86/pkeys: Add helper functions to update PKRU on the sigframe

[Thomas Gleixner]

On Thu, Aug 01 2024 at 06:51, Aruna Ramakrishna wrote:
>  
> +extern void __user *get_xsave_addr_user(struct xregs_state *xsave, int xfeature_nr);

  *xsave lacks __user

Thanks,

        tglx

Re: [PATCH v7 2/5] x86/pkeys: Add helper functions to update PKRU on the sigframe

[Aruna Ramakrishna]

> On Aug 1, 2024, at 1:57 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> 
> On Thu, Aug 01 2024 at 06:51, Aruna Ramakrishna wrote:
>> 
>> +extern void __user *get_xsave_addr_user(struct xregs_state *xsave, int xfeature_nr);
> 
>  *xsave lacks __user
> 
> Thanks,
> 
>        tglx

Thomas,

Sorry, that’s an oversight. I’ll add that.

Did you get a chance to review the rest of the patchset? If you have any
additional comments/suggestions, I can batch those fixes into v8.

Thanks!
Aruna

Re: [PATCH v7 2/5] x86/pkeys: Add helper functions to update PKRU on the sigframe

[Thomas Gleixner]

On Thu, Aug 01 2024 at 20:14, Aruna Ramakrishna wrote:
>> On Aug 1, 2024, at 1:57 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
>> On Thu, Aug 01 2024 at 06:51, Aruna Ramakrishna wrote:
>>> 
>>> +extern void __user *get_xsave_addr_user(struct xregs_state *xsave, int xfeature_nr);
>> 
>>  *xsave lacks __user
>> 
> Did you get a chance to review the rest of the patchset? If you have any
> additional comments/suggestions, I can batch those fixes into v8.

I did not find anything problematic.

If you spin up a V8 you could polish your changelogs a bit and give them
some structure. They mostly consist of one big lump. See:

  https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#changelog

for some examples.

Thanks,

        tglx