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Commit 882a0db9 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

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: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Reported-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reported-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/617
Link: https://lkml.kernel.org/r/5359166aad2d53f3145cd442d83d0e5115e0cd17.1564007838.git.jpoimboe@redhat.com
parent b68b9907

tools/objtool/check.c

+4 −3
Original line number Diff line number Diff line
@@ -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;

tools/objtool/check.h

+2 −1
Original line number Diff line number Diff line
@@ -33,8 +33,9 @@ struct instruction { 
	unsigned int len;

	enum insn_type type;

	unsigned long immediate;

	bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts;

	bool alt_group, dead_end, ignore, hint, save, restore, ignore_alts;

	bool retpoline_safe;

	u8 visited;

	struct symbol *call_dest;

	struct instruction *jump_dest;

	struct instruction *first_jump_src;