objtool: Improve UACCESS coverage
A clang build reported an (obvious) double CLAC while a GCC build did not;
it turns out that objtool only re-visits instructions if the first visit
was with AC=0. If OTOH the first visit was with AC=1, it completely ignores
any subsequent visit, even when it has AC=0.
Fix this by using a visited mask instead of a boolean, and (explicitly)
mark the AC state.
$ ./objtool check -b --no-fp --retpoline --uaccess drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x22: redundant UACCESS disable
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_copy_relocations.isra.34()+0xea: (alt)
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0xffffffffffffffff: (branch)
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_copy_relocations.isra.34()+0xd9: (alt)
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_copy_relocations.isra.34()+0xb2: (branch)
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_copy_relocations.isra.34()+0x39: (branch)
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_copy_relocations.isra.34()+0x0: <=== (func)
Reported-by: Josh Poimboeuf <[email protected]>
Reported-by: Thomas Gleixner <[email protected]>
Reported-by: Sedat Dilek <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Link: https://github.com/ClangBuiltLinux/linux/issues/617
Link: https://lkml.kernel.org/r/5359166aad2d53f3145cd442d83d0e5115e0cd17.1564007838.git.jpoimboe@redhat.com
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5f26620..176f2f0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1946,6 +1946,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
struct alternative *alt;
struct instruction *insn, *next_insn;
struct section *sec;
+ u8 visited;
int ret;
insn = first;
@@ -1972,12 +1973,12 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
return 1;
}
+ visited = 1 << state.uaccess;
if (insn->visited) {
if (!insn->hint && !insn_state_match(insn, &state))
return 1;
- /* If we were here with AC=0, but now have AC=1, go again */
- if (insn->state.uaccess || !state.uaccess)
+ if (insn->visited & visited)
return 0;
}
@@ -2024,7 +2025,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
} else
insn->state = state;
- insn->visited = true;
+ insn->visited |= visited;
if (!insn->ignore_alts) {
bool skip_orig = false;
