Commit 882a0db9 authored Jul 24, 2019 by Peter Zijlstra Committed by Thomas Gleixner Jul 25, 2019

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 <jpoimboe@redhat.com>
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat 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;

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