From 7616fc8bcd7ef4975a294337d6cd3007b8c18746 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Mon, 1 Jun 2015 10:47:40 +0100 Subject: arm64: alternative: Allow immediate branch as alternative instruction Since all 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 the target is outside of the replacement sequence). This patch handles the branch instructions in a different way, using the insn framework to recompute the immediate, and generate the right displacement in the above case. Acked-by: Will Deacon Signed-off-by: Marc Zyngier Signed-off-by: Catalin Marinas --- arch/arm64/kernel/alternative.c | 71 ++++++++++++++++++++++++++++++++++++++--- 1 file changed, 66 insertions(+), 5 deletions(-) (limited to 'arch') diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c index 28f8365edc4c..221b98312f0c 100644 --- a/arch/arm64/kernel/alternative.c +++ b/arch/arm64/kernel/alternative.c @@ -24,8 +24,13 @@ #include #include #include +#include #include +#define __ALT_PTR(a,f) (u32 *)((void *)&(a)->f + (a)->f) +#define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset) +#define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset) + extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; struct alt_region { @@ -33,13 +38,63 @@ struct alt_region { struct alt_instr *end; }; +/* + * Check if the target PC is within an alternative block. + */ +static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) +{ + unsigned long replptr; + + if (kernel_text_address(pc)) + return 1; + + replptr = (unsigned long)ALT_REPL_PTR(alt); + if (pc >= replptr && pc <= (replptr + alt->alt_len)) + return 0; + + /* + * Branching into *another* alternate sequence is doomed, and + * we're not even trying to fix it up. + */ + BUG(); +} + +static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr) +{ + u32 insn; + + insn = le32_to_cpu(*altinsnptr); + + if (aarch64_insn_is_branch_imm(insn)) { + s32 offset = aarch64_get_branch_offset(insn); + unsigned long target; + + target = (unsigned long)altinsnptr + offset; + + /* + * If we're branching inside the alternate sequence, + * do not rewrite the instruction, as it is already + * correct. Otherwise, generate the new instruction. + */ + if (branch_insn_requires_update(alt, target)) { + offset = target - (unsigned long)insnptr; + insn = aarch64_set_branch_offset(insn, offset); + } + } + + return insn; +} + static int __apply_alternatives(void *alt_region) { struct alt_instr *alt; struct alt_region *region = alt_region; - u8 *origptr, *replptr; + u32 *origptr, *replptr; for (alt = region->begin; alt < region->end; alt++) { + u32 insn; + int i, nr_inst; + if (!cpus_have_cap(alt->cpufeature)) continue; @@ -47,11 +102,17 @@ static int __apply_alternatives(void *alt_region) 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); + origptr = ALT_ORIG_PTR(alt); + replptr = ALT_REPL_PTR(alt); + nr_inst = alt->alt_len / sizeof(insn); + + for (i = 0; i < nr_inst; i++) { + insn = get_alt_insn(alt, origptr + i, replptr + i); + *(origptr + i) = cpu_to_le32(insn); + } + flush_icache_range((uintptr_t)origptr, - (uintptr_t)(origptr + alt->alt_len)); + (uintptr_t)(origptr + nr_inst)); } return 0; -- cgit v1.2.3