[PATCH v3 16/60] arm64: head: move relocation handling to C code

Ard Biesheuvel
2023-03-07T14:08:57Z

Now that we have a mini C runtime before the kernel mapping is up, we
can move the non-trivial relocation processing code out of head.S and
reimplement it in C.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/kernel/Makefile | 3 +-
arch/arm64/kernel/head.S | 104 ++------------------
arch/arm64/kernel/pi/Makefile | 5 +-
arch/arm64/kernel/pi/relocate.c | 62 ++++++++++++
arch/arm64/kernel/vmlinux.lds.S | 12 ++-
5 files changed, 82 insertions(+), 104 deletions(-)

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index ceba6792f5b3c473..e27168d6ed2050b9 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -58,7 +58,8 @@ obj-$(CONFIG_ACPI) += acpi.o
obj-$(CONFIG_ACPI_NUMA) += acpi_numa.o
obj-$(CONFIG_ARM64_ACPI_PARKING_PROTOCOL) += acpi_parking_protocol.o
obj-$(CONFIG_PARAVIRT) += paravirt.o
-obj-$(CONFIG_RANDOMIZE_BASE) += kaslr.o pi/
+obj-$(CONFIG_RELOCATABLE) += pi/
+obj-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
obj-$(CONFIG_HIBERNATION) += hibernate.o hibernate-asm.o
obj-$(CONFIG_ELF_CORE) += elfcore.o
obj-$(CONFIG_KEXEC_CORE) += machine_kexec.o relocate_kernel.o \
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 65cdaaa2c859418f..5047a2952ec273f9 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -81,7 +81,7 @@
* x20 primary_entry() .. __primary_switch() CPU boot mode
* x21 primary_entry() .. start_kernel() FDT pointer passed at boot in x0
* x22 create_idmap() .. start_kernel() ID map VA of the DT blob
- * x23 primary_entry() .. start_kernel() physical misalignment/KASLR offset
+ * x23 __primary_switch() physical misalignment/KASLR offset
* x24 __primary_switch() linear map KASLR seed
* x25 primary_entry() .. start_kernel() supported VA size
* x28 create_idmap() callee preserved temp register
@@ -389,7 +389,7 @@ SYM_FUNC_START_LOCAL(create_idmap)
/* Remap the kernel page tables r/w in the ID map */
adrp x1, _text
adrp x2, init_pg_dir
- adrp x3, init_pg_end
+ adrp x3, _end
bic x4, x2, #SWAPPER_BLOCK_SIZE - 1
mov x5, SWAPPER_RW_MMUFLAGS
mov x6, #SWAPPER_BLOCK_SHIFT
@@ -777,97 +777,6 @@ SYM_FUNC_START_LOCAL(__no_granule_support)
b 1b
SYM_FUNC_END(__no_granule_support)

-#ifdef CONFIG_RELOCATABLE
-SYM_FUNC_START_LOCAL(__relocate_kernel)
- /*
- * Iterate over each entry in the relocation table, and apply the
- * relocations in place.
- */
- adr_l x9, __rela_start
- adr_l x10, __rela_end
- mov_q x11, KIMAGE_VADDR // default virtual offset
- add x11, x11, x23 // actual virtual offset
-
-0: cmp x9, x10
- b.hs 1f
- ldp x12, x13, [x9], #24
- ldr x14, [x9, #-8]
- cmp w13, #R_AARCH64_RELATIVE
- b.ne 0b
- add x14, x14, x23 // relocate
- str x14, [x12, x23]
- b 0b
-
-1:
-#ifdef CONFIG_RELR
- /*
- * Apply RELR relocations.
- *
- * RELR is a compressed format for storing relative relocations. The
- * encoded sequence of entries looks like:
- * [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
- *
- * i.e. start with an address, followed by any number of bitmaps. The
- * address entry encodes 1 relocation. The subsequent bitmap entries
- * encode up to 63 relocations each, at subsequent offsets following
- * the last address entry.
- *
- * The bitmap entries must have 1 in the least significant bit. The
- * assumption here is that an address cannot have 1 in lsb. Odd
- * addresses are not supported. Any odd addresses are stored in the RELA
- * section, which is handled above.
- *
- * Excluding the least significant bit in the bitmap, each non-zero
- * bit in the bitmap represents a relocation to be applied to
- * a corresponding machine word that follows the base address
- * word. The second least significant bit represents the machine
- * word immediately following the initial address, and each bit
- * that follows represents the next word, in linear order. As such,
- * a single bitmap can encode up to 63 relocations in a 64-bit object.
- *
- * In this implementation we store the address of the next RELR table
- * entry in x9, the address being relocated by the current address or
- * bitmap entry in x13 and the address being relocated by the current
- * bit in x14.
- */
- adr_l x9, __relr_start
- adr_l x10, __relr_end
-
-2: cmp x9, x10
- b.hs 7f
- ldr x11, [x9], #8
- tbnz x11, #0, 3f // branch to handle bitmaps
- add x13, x11, x23
- ldr x12, [x13] // relocate address entry
- add x12, x12, x23
- str x12, [x13], #8 // adjust to start of bitmap
- b 2b
-
-3: mov x14, x13
-4: lsr x11, x11, #1
- cbz x11, 6f
- tbz x11, #0, 5f // skip bit if not set
- ldr x12, [x14] // relocate bit
- add x12, x12, x23
- str x12, [x14]
-
-5: add x14, x14, #8 // move to next bit's address
- b 4b
-
-6: /*
- * Move to the next bitmap's address. 8 is the word size, and 63 is the
- * number of significant bits in a bitmap entry.
- */
- add x13, x13, #(8 * 63)
- b 2b
-
-7:
-#endif
- ret
-
-SYM_FUNC_END(__relocate_kernel)
-#endif
-
SYM_FUNC_START_LOCAL(__primary_switch)
adrp x1, reserved_pg_dir
adrp x2, init_idmap_pg_dir
@@ -875,11 +784,11 @@ SYM_FUNC_START_LOCAL(__primary_switch)
#ifdef CONFIG_RELOCATABLE
adrp x23, KERNEL_START
and x23, x23, MIN_KIMG_ALIGN - 1
-#ifdef CONFIG_RANDOMIZE_BASE
- mov x0, x22
- adrp x1, init_pg_end
+ adrp x1, early_init_stack
mov sp, x1
mov x29, xzr
+#ifdef CONFIG_RANDOMIZE_BASE
+ mov x0, x22
bl __pi_kaslr_early_init
and x24, x0, #SZ_2M - 1 // capture memstart offset seed
bic x0, x0, #SZ_2M - 1
@@ -892,7 +801,8 @@ SYM_FUNC_START_LOCAL(__primary_switch)
adrp x1, init_pg_dir
load_ttbr1 x1, x1, x2
#ifdef CONFIG_RELOCATABLE
- bl __relocate_kernel
+ mov x0, x23
+ bl __pi_relocate_kernel
#endif
ldr x8, =__primary_switched
adrp x0, KERNEL_START // __pa(KERNEL_START)
diff --git a/arch/arm64/kernel/pi/Makefile b/arch/arm64/kernel/pi/Makefile
index 2bbe866417d453ff..d084c1dcf4165420 100644
--- a/arch/arm64/kernel/pi/Makefile
+++ b/arch/arm64/kernel/pi/Makefile
@@ -38,5 +38,6 @@ $(obj)/lib-%.pi.o: OBJCOPYFLAGS += --prefix-alloc-sections=.init
$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
$(call if_changed_rule,cc_o_c)

-obj-y := kaslr_early.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
-extra-y := $(patsubst %.pi.o,%.o,$(obj-y))
+obj-y := relocate.pi.o
+obj-$(CONFIG_RANDOMIZE_BASE) += kaslr_early.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
+extra-y := $(patsubst %.pi.o,%.o,$(obj-y))
diff --git a/arch/arm64/kernel/pi/relocate.c b/arch/arm64/kernel/pi/relocate.c
new file mode 100644
index 0000000000000000..1853408ea76b0e5d
--- /dev/null
+++ b/arch/arm64/kernel/pi/relocate.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2023 Google LLC
+// Authors: Ard Biesheuvel <ardb@google.com>
+// Peter Collingbourne <pcc@google.com>
+
+#include <linux/elf.h>
+#include <linux/init.h>
+#include <linux/types.h>
+
+extern const Elf64_Rela rela_start[], rela_end[];
+extern const u64 relr_start[], relr_end[];
+
+void __init relocate_kernel(u64 offset)
+{
+ u64 *place = NULL;
+
+ for (const Elf64_Rela *rela = rela_start; rela < rela_end; rela++) {
+ if (ELF64_R_TYPE(rela->r_info) != R_AARCH64_RELATIVE)
+ continue;
+ *(u64 *)(rela->r_offset + offset) = rela->r_addend + offset;
+ }
+
+ if (!IS_ENABLED(CONFIG_RELR) || !offset)
+ return;
+
+ /*
+ * Apply RELR relocations.
+ *
+ * RELR is a compressed format for storing relative relocations. The
+ * encoded sequence of entries looks like:
+ * [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
+ *
+ * i.e. start with an address, followed by any number of bitmaps. The
+ * address entry encodes 1 relocation. The subsequent bitmap entries
+ * encode up to 63 relocations each, at subsequent offsets following
+ * the last address entry.
+ *
+ * The bitmap entries must have 1 in the least significant bit. The
+ * assumption here is that an address cannot have 1 in lsb. Odd
+ * addresses are not supported. Any odd addresses are stored in the
+ * RELA section, which is handled above.
+ *
+ * With the exception of the least significant bit, each bit in the
+ * bitmap corresponds with a machine word that follows the base address
+ * word, and the bit value indicates whether or not a relocation needs
+ * to be applied to it. The second least significant bit represents the
+ * machine word immediately following the initial address, and each bit
+ * that follows represents the next word, in linear order. As such, a
+ * single bitmap can encode up to 63 relocations in a 64-bit object.
+ */
+ for (const u64 *relr = relr_start; relr < relr_end; relr++) {
+ if ((*relr & 1) == 0) {
+ place = (u64 *)(*relr + offset);
+ *place++ += offset;
+ } else {
+ for (u64 *p = place, r = *relr >> 1; r; p++, r >>= 1)
+ if (r & 1)
+ *p += offset;
+ place += 63;
+ }
+ }
+}
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index b9202c2ee18e02d8..ec24b1e70d606ec8 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -271,15 +271,15 @@ SECTIONS
HYPERVISOR_RELOC_SECTION

.rela.dyn : ALIGN(8) {
- __rela_start = .;
+ __pi_rela_start = .;
*(.rela .rela*)
- __rela_end = .;
+ __pi_rela_end = .;
}

.relr.dyn : ALIGN(8) {
- __relr_start = .;
+ __pi_relr_start = .;
*(.relr.dyn)
- __relr_end = .;
+ __pi_relr_end = .;
}

. = ALIGN(SEGMENT_ALIGN);
@@ -318,6 +318,10 @@ SECTIONS
init_pg_dir = .;
. += INIT_DIR_SIZE;
init_pg_end = .;
+#ifdef CONFIG_RELOCATABLE
+ . += SZ_4K; /* stack for the early relocation code */
+ early_init_stack = .;
+#endif

. = ALIGN(SEGMENT_ALIGN);
__pecoff_data_size = ABSOLUTE(. - __initdata_begin);
--
2.39.2