linux-kernel - [PATCH v3 2/3] x86: Use static_cpu_has in uaccess region to avoid instrumentation

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Message-Id: <20190531150828.157832-3-elver@google.com>
Date:   Fri, 31 May 2019 17:08:30 +0200
From:   Marco Elver <elver@...gle.com>
To:     peterz@...radead.org, aryabinin@...tuozzo.com, dvyukov@...gle.com,
        glider@...gle.com, andreyknvl@...gle.com, mark.rutland@....com,
        hpa@...or.com
Cc:     corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        x86@...nel.org, arnd@...db.de, jpoimboe@...hat.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, kasan-dev@...glegroups.com,
        Marco Elver <elver@...gle.com>
Subject: [PATCH v3 2/3] x86: Use static_cpu_has in uaccess region to avoid instrumentation

This patch is a pre-requisite for enabling KASAN bitops instrumentation;
using static_cpu_has instead of boot_cpu_has avoids instrumentation of
test_bit inside the uaccess region. With instrumentation, the KASAN
check would otherwise be flagged by objtool.

For consistency, kernel/signal.c was changed to mirror this change,
however, is never instrumented with KASAN (currently unsupported under
x86 32bit).

Signed-off-by: Marco Elver <elver@...gle.com>
Suggested-by: H. Peter Anvin <hpa@...or.com>
---
Changes in v3:
* Use static_cpu_has instead of moving boot_cpu_has outside uaccess
  region.

Changes in v2:
* Replaces patch: 'tools/objtool: add kasan_check_* to uaccess
  whitelist'
---
 arch/x86/ia32/ia32_signal.c | 2 +-
 arch/x86/kernel/signal.c    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 629d1ee05599..1cee10091b9f 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -358,7 +358,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
 		put_user_ex(ptr_to_compat(&frame->uc), &frame->puc);
 
 		/* Create the ucontext.  */
-		if (boot_cpu_has(X86_FEATURE_XSAVE))
+		if (static_cpu_has(X86_FEATURE_XSAVE))
 			put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
 		else
 			put_user_ex(0, &frame->uc.uc_flags);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 364813cea647..52eb1d551aed 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -391,7 +391,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
 		put_user_ex(&frame->uc, &frame->puc);
 
 		/* Create the ucontext.  */
-		if (boot_cpu_has(X86_FEATURE_XSAVE))
+		if (static_cpu_has(X86_FEATURE_XSAVE))
 			put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
 		else
 			put_user_ex(0, &frame->uc.uc_flags);
-- 
2.22.0.rc1.257.g3120a18244-goog