powerpc/lib: Fix off-by-one in alternate feature patching

commit b8858581febb050688e276b956796bc4a78299ed upstream.

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 <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index a95ea007d654d5db2b78d811a4ef21a750a95609..d0c0b8443dcfc0e6e56a347a449d65db9640193b 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;