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: 3951f43dfd56 ("KVM: PPC: Book3S HV: Branch inside feature section")
Fixes: 08ca55e2ce94 ("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>

diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index 35f80ab7cbd83c6fbd7eca53955d4e14839ff837..288fe4f0db4ea326321915e1904da3771380978d 100644 (file)
--- 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;