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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: d20fe50a7b ("KVM: PPC: Book3S HV: Branch inside feature section")
Fixes: 9b1a735de6 ("powerpc: Add logic to patch alternative feature sections")
Cc: stable@vger.kernel.org # v2.6.27+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Michael Ellerman 2018-04-16 23:25:19 +10:00
parent 60cc43fc88
commit b8858581fe
1 changed files with 1 additions and 1 deletions
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2
arch/powerpc/lib/feature-fixups.c
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@ -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;