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authorMarc Zyngier <marc.zyngier@arm.com>2015-03-27 13:09:22 +0000
committerWill Deacon <will.deacon@arm.com>2015-03-30 11:03:43 +0100
commitfef7f2b2010381c795ae43743ad31931cc58f5ad (patch)
treeb8f144d8646b22385f3e5ff603749cd26eb09703 /arch/arm64/kernel/alternative.c
parent0978fb25f86b7595821cee6955679250d47c6438 (diff)
arm64: alternative: Allow immediate branch as alternative instruction
Since all immediate branches are PC-relative on Aarch64, these instructions cannot be used as an alternative with the simplistic approach we currently have (the immediate has been computed from the .altinstr_replacement section, and end-up being completely off if we insert it directly). This patch handles the b and bl instructions in a different way, using the insn framework to recompute the immediate, and generate the right displacement. Reviewed-by: Andre Przywara <andre.przywara@arm.com> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/kernel/alternative.c')
-rw-r--r--arch/arm64/kernel/alternative.c55
1 files changed, 53 insertions, 2 deletions
diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index ad7821d64a1d..21033bba9390 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -24,6 +24,7 @@
#include <asm/cacheflush.h>
#include <asm/alternative.h>
#include <asm/cpufeature.h>
+#include <asm/insn.h>
#include <linux/stop_machine.h>
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
@@ -33,6 +34,48 @@ struct alt_region {
struct alt_instr *end;
};
+/*
+ * Decode the imm field of a b/bl instruction, and return the byte
+ * offset as a signed value (so it can be used when computing a new
+ * branch target).
+ */
+static s32 get_branch_offset(u32 insn)
+{
+ s32 imm = aarch64_insn_decode_immediate(AARCH64_INSN_IMM_26, insn);
+
+ /* sign-extend the immediate before turning it into a byte offset */
+ return (imm << 6) >> 4;
+}
+
+static u32 get_alt_insn(u8 *insnptr, u8 *altinsnptr)
+{
+ u32 insn;
+
+ aarch64_insn_read(altinsnptr, &insn);
+
+ /* Stop the world on instructions we don't support... */
+ BUG_ON(aarch64_insn_is_cbz(insn));
+ BUG_ON(aarch64_insn_is_cbnz(insn));
+ BUG_ON(aarch64_insn_is_bcond(insn));
+ /* ... and there is probably more. */
+
+ if (aarch64_insn_is_b(insn) || aarch64_insn_is_bl(insn)) {
+ enum aarch64_insn_branch_type type;
+ unsigned long target;
+
+ if (aarch64_insn_is_b(insn))
+ type = AARCH64_INSN_BRANCH_NOLINK;
+ else
+ type = AARCH64_INSN_BRANCH_LINK;
+
+ target = (unsigned long)altinsnptr + get_branch_offset(insn);
+ insn = aarch64_insn_gen_branch_imm((unsigned long)insnptr,
+ target, type);
+ }
+
+ return insn;
+}
+
static int __apply_alternatives(void *alt_region)
{
struct alt_instr *alt;
@@ -40,16 +83,24 @@ static int __apply_alternatives(void *alt_region)
u8 *origptr, *replptr;
for (alt = region->begin; alt < region->end; alt++) {
+ u32 insn;
+ int i;
+
if (!cpus_have_cap(alt->cpufeature))
continue;
- BUG_ON(alt->alt_len > alt->orig_len);
+ BUG_ON(alt->alt_len != alt->orig_len);
pr_info_once("patching kernel code\n");
origptr = (u8 *)&alt->orig_offset + alt->orig_offset;
replptr = (u8 *)&alt->alt_offset + alt->alt_offset;
- memcpy(origptr, replptr, alt->alt_len);
+
+ for (i = 0; i < alt->alt_len; i += sizeof(insn)) {
+ insn = get_alt_insn(origptr + i, replptr + i);
+ aarch64_insn_write(origptr + i, insn);
+ }
+
flush_icache_range((uintptr_t)origptr,
(uintptr_t)(origptr + alt->alt_len));
}