From: Michael Ellerman Date: Fri, 22 May 2020 13:33:18 +0000 (+1000) Subject: powerpc: Add ppc_inst_next() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=c5ff46d69c410f7fac173e4fde3eea484b4b4eda;p=linux.git powerpc: Add ppc_inst_next() In a few places we want to calculate the address of the next instruction. Previously that was simple, we just added 4 bytes, or if using a u32 * we incremented that pointer by 1. But prefixed instructions make it more complicated, we need to advance by either 4 or 8 bytes depending on the actual instruction. We also can't do pointer arithmetic using struct ppc_inst, because it is always 8 bytes in size on 64-bit, even though we might only need to advance by 4 bytes. So add a ppc_inst_next() helper which calculates the location of the next instruction, if the given instruction was located at the given address. Note the instruction doesn't need to actually be at the address in memory. Although it would seem natural for the value to be passed by value, that makes it too easy to write a loop that will read off the end of a page, eg: for (; src < end; src = ppc_inst_next(src, *src), dest = ppc_inst_next(dest, *dest)) As noticed by Christophe and Jordan, if end is the exact end of a page, and the next page is not mapped, this will fault, because *dest will read 8 bytes, 4 bytes into the next page. So value is passed by reference, so the helper can be careful to use ppc_inst_read() on it. Signed-off-by: Michael Ellerman Reviewed-by: Jordan Niethe Link: https://lore.kernel.org/r/20200522133318.1681406-1-mpe@ellerman.id.au --- diff --git a/arch/powerpc/include/asm/inst.h b/arch/powerpc/include/asm/inst.h index d82e0c99cfa10..5b756ba77ed2e 100644 --- a/arch/powerpc/include/asm/inst.h +++ b/arch/powerpc/include/asm/inst.h @@ -100,6 +100,19 @@ static inline int ppc_inst_len(struct ppc_inst x) return ppc_inst_prefixed(x) ? 8 : 4; } +/* + * Return the address of the next instruction, if the instruction @value was + * located at @location. + */ +static inline struct ppc_inst *ppc_inst_next(void *location, struct ppc_inst *value) +{ + struct ppc_inst tmp; + + tmp = ppc_inst_read(value); + + return location + ppc_inst_len(tmp); +} + int probe_user_read_inst(struct ppc_inst *inst, struct ppc_inst __user *nip); diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c index 83e883e1a42db..d200e7df71678 100644 --- a/arch/powerpc/kernel/uprobes.c +++ b/arch/powerpc/kernel/uprobes.c @@ -112,7 +112,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) * support doesn't exist and have to fix-up the next instruction * to be executed. */ - regs->nip = utask->vaddr + ppc_inst_len(ppc_inst_read(&auprobe->insn)); + regs->nip = (unsigned long)ppc_inst_next((void *)utask->vaddr, &auprobe->insn); user_disable_single_step(current); return 0; diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c index 80f320c2e1892..4c0a7ee9fa000 100644 --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -68,7 +68,7 @@ static int patch_alt_instruction(struct ppc_inst *src, struct ppc_inst *dest, static int patch_feature_section(unsigned long value, struct fixup_entry *fcur) { - struct ppc_inst *start, *end, *alt_start, *alt_end, *src, *dest; + struct ppc_inst *start, *end, *alt_start, *alt_end, *src, *dest, nop; start = calc_addr(fcur, fcur->start_off); end = calc_addr(fcur, fcur->end_off); @@ -84,14 +84,15 @@ static int patch_feature_section(unsigned long value, struct fixup_entry *fcur) src = alt_start; dest = start; - for (; src < alt_end; src = (void *)src + ppc_inst_len(ppc_inst_read(src)), - (dest = (void *)dest + ppc_inst_len(ppc_inst_read(dest)))) { + for (; src < alt_end; src = ppc_inst_next(src, src), + dest = ppc_inst_next(dest, dest)) { if (patch_alt_instruction(src, dest, alt_start, alt_end)) return 1; } - for (; dest < end; dest = (void *)dest + ppc_inst_len(ppc_inst(PPC_INST_NOP))) - raw_patch_instruction(dest, ppc_inst(PPC_INST_NOP)); + nop = ppc_inst(PPC_INST_NOP); + for (; dest < end; dest = ppc_inst_next(dest, &nop)) + raw_patch_instruction(dest, nop); return 0; } @@ -405,8 +406,8 @@ static void do_final_fixups(void) while (src < end) { inst = ppc_inst_read(src); raw_patch_instruction(dest, inst); - src = (void *)src + ppc_inst_len(inst); - dest = (void *)dest + ppc_inst_len(inst); + src = ppc_inst_next(src, src); + dest = ppc_inst_next(dest, dest); } #endif } diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index de585204d1d26..16ee6639a60cb 100644 --- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c @@ -939,7 +939,7 @@ static void insert_bpts(void) } patch_instruction(bp->instr, instr); - patch_instruction((void *)bp->instr + ppc_inst_len(instr), + patch_instruction(ppc_inst_next(bp->instr, &instr), ppc_inst(bpinstr)); if (bp->enabled & BP_CIABR) continue;