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From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	x86@kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH] objtool: Improve UACCESS coverage
Date: Wed, 24 Jul 2019 18:48:21 +0200	[thread overview]
Message-ID: <20190724164821.GB31425@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190724141040.GA31425@hirez.programming.kicks-ass.net>

On Wed, Jul 24, 2019 at 04:10:40PM +0200, Peter Zijlstra wrote:
> And that most certainly should trigger...
> 
> Let me gdb that objtool thing.

---
Subject: objtool: Improve UACCESS coverage

A clang build reported an (obvious) double CLAC while a GCC build did
not; it turns out we only re-visit instructions if the first visit was
with AC=0. If OTOH the first visit was with AC=1, we completely ignore
any subsequent visit, even when it has AC=0.

Fix this by using a visited mask, instead of boolean and (explicitly)
mark the AC state.

$ ./objtool check -b --no-fp --retpoline --uaccess ../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o
../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x22: redundant UACCESS disable
../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:   eb_copy_relocations.isra.34()+0xea: (alt)
../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:   .altinstr_replacement+0xffffffffffffffff: (branch)
../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:   eb_copy_relocations.isra.34()+0xd9: (alt)
../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:   eb_copy_relocations.isra.34()+0xb2: (branch)
../../defconfig-build/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:   eb_copy_relocations.isra.34()+0x39: (branch)
../../defconfig-build/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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 tools/objtool/check.c | 7 ++++---
 tools/objtool/check.h | 3 ++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5f26620f13f5..176f2f084060 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;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index b881fafcf55d..6d875ca6fce0 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -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;

  reply	other threads:[~2019-07-24 16:48 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-18 20:40 x86 - clang / objtool status Thomas Gleixner
2019-07-18 20:58 ` Nathan Chancellor
2019-07-19  6:39   ` Thomas Gleixner
2019-07-19  7:00     ` Arnd Bergmann
2019-07-19  7:03     ` Nathan Chancellor
2019-07-24 16:57     ` Nick Desaulniers
2019-07-18 22:42 ` Nick Desaulniers
2019-07-19  6:44   ` Thomas Gleixner
2019-07-19 11:37 ` Sedat Dilek
2019-07-19 13:48   ` Sedat Dilek
2019-07-22 15:40     ` Sedat Dilek
2019-07-25  6:17       ` Sedat Dilek
2019-07-24  2:43 ` Josh Poimboeuf
2019-07-24  7:47   ` Peter Zijlstra
2019-07-24 12:37     ` Josh Poimboeuf
2019-07-24 12:55     ` Josh Poimboeuf
2019-07-24 13:35       ` Peter Zijlstra
2019-07-24 14:05         ` Josh Poimboeuf
2019-07-24 14:10         ` Peter Zijlstra
2019-07-24 16:48           ` Peter Zijlstra [this message]
2019-07-24 16:54             ` [PATCH] objtool: Improve UACCESS coverage Nathan Chancellor
2019-07-24 16:55             ` Nick Desaulniers
2019-07-24 18:30             ` Sedat Dilek
2019-07-24 18:32               ` Sedat Dilek
2019-07-24 16:52   ` x86 - clang / objtool status Peter Zijlstra
2019-07-24 17:22   ` Nick Desaulniers

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