linux-kernel - [PATCH AUTOSEL 5.2 77/85] objtool: Add mcsafe_handle

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Message-Id: <20190726133936.11177-77-sashal@kernel.org>
Date:   Fri, 26 Jul 2019 09:39:27 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.2 77/85] objtool: Add mcsafe_handle_tail() to the uaccess safe list

From: Josh Poimboeuf <jpoimboe@...hat.com>

[ Upstream commit a7e47f26039c26312a4144c3001b4e9fa886bd45 ]

After an objtool improvement, it's reporting that __memcpy_mcsafe() is
calling mcsafe_handle_tail() with AC=1:

  arch/x86/lib/memcpy_64.o: warning: objtool: .fixup+0x13: call to mcsafe_handle_tail() with UACCESS enabled
  arch/x86/lib/memcpy_64.o: warning: objtool:   __memcpy_mcsafe()+0x34: (alt)
  arch/x86/lib/memcpy_64.o: warning: objtool:   __memcpy_mcsafe()+0xb: (branch)
  arch/x86/lib/memcpy_64.o: warning: objtool:   __memcpy_mcsafe()+0x0: <=== (func)

mcsafe_handle_tail() is basically an extension of __memcpy_mcsafe(), so
AC=1 is supposed to be set.  Add mcsafe_handle_tail() to the uaccess
safe list.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/035c38f7eac845281d3c3d36749144982e06e58c.1563413318.git.jpoimboe@redhat.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/objtool/check.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 172f99195726..f5c3b97051a7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -488,6 +488,7 @@ static const char *uaccess_safe_builtin[] = {
 	/* misc */
 	"csum_partial_copy_generic",
 	"__memcpy_mcsafe",
+	"mcsafe_handle_tail",
 	"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 	NULL
 };
-- 
2.20.1