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From: Marco Elver <elver@google.com>
To: peterz@infradead.org, aryabinin@virtuozzo.com,
	dvyukov@google.com, glider@google.com, andreyknvl@google.com,
	mark.rutland@arm.com
Cc: corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, hpa@zytor.com, x86@kernel.org, arnd@arndb.de,
	jpoimboe@redhat.com, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	kasan-dev@googlegroups.com, Marco Elver <elver@google.com>
Subject: [PATCH 2/3] x86: Move CPU feature test out of uaccess region
Date: Wed, 29 May 2019 16:15:00 +0200	[thread overview]
Message-ID: <20190529141500.193390-3-elver@google.com> (raw)
In-Reply-To: <20190529141500.193390-1-elver@google.com>

This patch is a pre-requisite for enabling KASAN bitops instrumentation:
moves boot_cpu_has feature test out of the uaccess region, as
boot_cpu_has uses test_bit. With instrumentation, the KASAN check would
otherwise be flagged by objtool.

This approach is preferred over adding the explicit kasan_check_*
functions to the uaccess whitelist of objtool, as the case here appears
to be the only one.

Signed-off-by: Marco Elver <elver@google.com>
---
v1:
* This patch replaces patch: 'tools/objtool: add kasan_check_* to
  uaccess whitelist'
---
 arch/x86/ia32/ia32_signal.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 629d1ee05599..12264e3c9c43 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -333,6 +333,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
 	void __user *restorer;
 	int err = 0;
 	void __user *fpstate = NULL;
+	bool has_xsave;
 
 	/* __copy_to_user optimizes that into a single 8 byte store */
 	static const struct {
@@ -352,13 +353,19 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
 	if (!access_ok(frame, sizeof(*frame)))
 		return -EFAULT;
 
+	/*
+	 * Move non-uaccess accesses out of uaccess region if not strictly
+	 * required; this also helps avoid objtool flagging these accesses with
+	 * instrumentation enabled.
+	 */
+	has_xsave = boot_cpu_has(X86_FEATURE_XSAVE);
 	put_user_try {
 		put_user_ex(sig, &frame->sig);
 		put_user_ex(ptr_to_compat(&frame->info), &frame->pinfo);
 		put_user_ex(ptr_to_compat(&frame->uc), &frame->puc);
 
 		/* Create the ucontext.  */
-		if (boot_cpu_has(X86_FEATURE_XSAVE))
+		if (has_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


  parent reply	other threads:[~2019-05-29 14:23 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 14:14 [PATCH v2 0/3] Bitops instrumentation for KASAN Marco Elver
2019-05-29 14:14 ` [PATCH v2 1/3] lib/test_kasan: Add bitops tests Marco Elver
2019-05-29 15:15   ` Mark Rutland
2019-05-29 14:15 ` Marco Elver [this message]
2019-05-29 14:29   ` [PATCH 2/3] x86: Move CPU feature test out of uaccess region hpa
2019-05-31  9:57     ` Marco Elver
2019-05-31 23:41       ` hpa
2019-06-03  9:03         ` Marco Elver
2019-05-29 14:15 ` [PATCH v2 3/3] asm-generic, x86: Add bitops instrumentation for KASAN Marco Elver
2019-05-29 15:32   ` Mark Rutland
2019-05-29 15:40     ` Marco Elver
2019-05-31 15:12 ` [PATCH v2 0/3] Bitops " Marco Elver

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