From b8858581febb050688e276b956796bc4a78299ed Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Mon, 16 Apr 2018 23:25:19 +1000 Subject: [PATCH] powerpc/lib: Fix off-by-one in alternate feature patching When we patch an alternate feature section, we have to adjust any relative branches that branch out of the alternate section. But currently we have a bug if we have a branch that points to past the last instruction of the alternate section, eg: FTR_SECTION_ELSE 1: b 2f or 6,6,6 2: ALT_FTR_SECTION_END(...) nop This will result in a relative branch at 1 with a target that equals the end of the alternate section. That branch does not need adjusting when it's moved to the non-else location. Currently we do adjust it, resulting in a branch that goes off into the link-time location of the else section, which is junk. The fix is to not patch branches that have a target == end of the alternate section. Fixes: d20fe50a7b3c ("KVM: PPC: Book3S HV: Branch inside feature section") Fixes: 9b1a735de64c ("powerpc: Add logic to patch alternative feature sections") Cc: stable@vger.kernel.org # v2.6.27+ Signed-off-by: Michael Ellerman --- arch/powerpc/lib/feature-fixups.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c index 35f80ab..288fe4f 100644 --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -55,7 +55,7 @@ static int patch_alt_instruction(unsigned int *src, unsigned int *dest, unsigned int *target = (unsigned int *)branch_target(src); /* Branch within the section doesn't need translating */ - if (target < alt_start || target >= alt_end) { + if (target < alt_start || target > alt_end) { instr = translate_branch(dest, src); if (!instr) return 1; -- 2.7.4