Date:   Tue, 14 Dec 2021 17:20:30 +0100
In-Reply-To: <20211214162050.660953-1-glider@google.com>
Message-Id: <20211214162050.660953-24-glider@google.com>
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References: <20211214162050.660953-1-glider@google.com>
Subject: [PATCH 23/43] kmsan: make READ_ONCE_TASK_STACK() return initialized values
From:   Alexander Potapenko <glider@google.com>
To:     glider@google.com
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Marco Elver <elver@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

To avoid false positives, assume that reading from the task stack
always produces initialized values.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
Link: https://linux-review.googlesource.com/id/I9e2350bf3e88688dd83537e12a23456480141997
---
 arch/x86/include/asm/unwind.h | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index 2a1f8734416dc..51173b19ac4d5 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -129,18 +129,19 @@ unsigned long unwind_recover_ret_addr(struct unwind_state *state,
 }
 
 /*
- * This disables KASAN checking when reading a value from another task's stack,
- * since the other task could be running on another CPU and could have poisoned
- * the stack in the meantime.
+ * This disables KASAN/KMSAN checking when reading a value from another task's
+ * stack, since the other task could be running on another CPU and could have
+ * poisoned the stack in the meantime. Frame pointers are uninitialized by
+ * default, so for KMSAN we mark the return value initialized unconditionally.
  */
-#define READ_ONCE_TASK_STACK(task, x)			\
-({							\
-	unsigned long val;				\
-	if (task == current)				\
-		val = READ_ONCE(x);			\
-	else						\
-		val = READ_ONCE_NOCHECK(x);		\
-	val;						\
+#define READ_ONCE_TASK_STACK(task, x)				\
+({								\
+	unsigned long val;					\
+	if (task == current && !IS_ENABLED(CONFIG_KMSAN))	\
+		val = READ_ONCE(x);				\
+	else							\
+		val = READ_ONCE_NOCHECK(x);			\
+	val;							\
 })
 
 static inline bool task_on_another_cpu(struct task_struct *task)
-- 
2.34.1.173.g76aa8bc2d0-goog