From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
Linus Torvalds <torvalds@linux-foundation.org>,
dja@axtens.net, linux-kernel@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, christophe.leroy@c-s.fr,
linux-arch@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
Segher Boessenkool <segher@kernel.crashing.org>,
Arnd Bergmann <arnd@arndb.de>,
Christian Borntraeger <borntraeger@de.ibm.com>
Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops))
Date: Thu, 12 Dec 2019 11:46:10 +0100 [thread overview]
Message-ID: <20191212104610.GW2827@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191212100756.GA11317@willie-the-truck>
On Thu, Dec 12, 2019 at 10:07:56AM +0000, Will Deacon wrote:
> > So your proposed change _should_ be fine. Will, I'm assuming you never
> > saw this on your ARGH64 builds when you did this code ?
>
> I did see it, but (a) looking at the code out-of-line makes it look a lot
> worse than it actually is (so the ext4 example is really helpful -- thanks
> Michael!) and (b) I chalked it up to a crappy compiler.
>
> However, see this comment from Arnd on my READ_ONCE series from the other
> day:
>
> https://lore.kernel.org/lkml/CAK8P3a0f=WvSQSBQ4t0FmEkcFE_mC3oARxaeTviTSkSa-D2qhg@mail.gmail.com
>
> In which case, I'm thinking that we should be doing better in READ_ONCE()
> for non-buggy compilers which would also keep the KCSAN folks happy for this
> code (and would help with [1] too).
So something like this then? Although I suppose that should be moved
into compiler-gcc.h and then guarded by #ifndef READ_ONCE or so.
---
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index ad8c76144a3c..8326e2cf28b4 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -179,20 +179,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
#include <uapi/linux/types.h>
#include <linux/kcsan-checks.h>
-
-#define __READ_ONCE_SIZE \
-({ \
- switch (size) { \
- case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \
- case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \
- case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \
- case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \
- default: \
- barrier(); \
- __builtin_memcpy((void *)res, (const void *)p, size); \
- barrier(); \
- } \
-})
+#include <asm/barrier.h>
+#include <linux/kasan-checks.h>
#ifdef CONFIG_KASAN
/*
@@ -222,6 +210,22 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
#define __no_sanitize_or_inline __always_inline
#endif
+#ifdef GCC_VERSION < 40800
+
+#define __READ_ONCE_SIZE \
+({ \
+ switch (size) { \
+ case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \
+ case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \
+ case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \
+ case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \
+ default: \
+ barrier(); \
+ __builtin_memcpy((void *)res, (const void *)p, size); \
+ barrier(); \
+ } \
+})
+
static __no_kcsan_or_inline
void __read_once_size(const volatile void *p, void *res, int size)
{
@@ -274,9 +278,6 @@ void __write_once_size(volatile void *p, void *res, int size)
* with an explicit memory barrier or atomic instruction that provides the
* required ordering.
*/
-#include <asm/barrier.h>
-#include <linux/kasan-checks.h>
-
#define __READ_ONCE(x, check) \
({ \
union { typeof(x) __val; char __c[1]; } __u; \
@@ -295,6 +296,23 @@ void __write_once_size(volatile void *p, void *res, int size)
*/
#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
+#else /* GCC_VERSION < 40800 */
+
+#define READ_ONCE_NOCHECK(x) \
+({ \
+ typeof(x) __x = *(volatile typeof(x))&(x); \
+ smp_read_barrier_depends(); \
+ __x;
+})
+
+#define READ_ONCE(x) \
+({ \
+ kcsan_check_atomic_read(&(x), sizeof(x)); \
+ READ_ONCE_NOCHECK(x); \
+})
+
+#endif /* GCC_VERSION < 40800 */
+
static __no_kasan_or_inline
unsigned long read_word_at_a_time(const void *addr)
{
next prev parent reply other threads:[~2019-12-12 10:46 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-06 12:46 [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) Michael Ellerman
2019-12-06 13:16 ` Peter Zijlstra
2019-12-10 5:38 ` Michael Ellerman
2019-12-10 10:15 ` Peter Zijlstra
2019-12-11 0:29 ` Michael Ellerman
2019-12-12 5:42 ` READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Michael Ellerman
2019-12-12 8:01 ` Peter Zijlstra
2019-12-12 10:07 ` Will Deacon
2019-12-12 10:46 ` Peter Zijlstra [this message]
2019-12-12 17:04 ` Will Deacon
2019-12-12 17:16 ` Will Deacon
2019-12-12 17:41 ` Linus Torvalds
2019-12-12 17:50 ` Segher Boessenkool
2019-12-12 18:06 ` Will Deacon
2019-12-12 18:29 ` Christian Borntraeger
2019-12-12 18:43 ` Linus Torvalds
2019-12-12 19:34 ` Will Deacon
2019-12-12 20:21 ` Peter Zijlstra
2019-12-12 20:53 ` Peter Zijlstra
2019-12-13 10:47 ` Luc Van Oostenryck
2019-12-13 12:56 ` Peter Zijlstra
2019-12-13 14:28 ` Luc Van Oostenryck
2019-12-12 20:49 ` Linus Torvalds
2019-12-13 13:17 ` Arnd Bergmann
2019-12-13 21:32 ` Arnd Bergmann
2019-12-13 22:01 ` Linus Torvalds
2019-12-16 10:28 ` Will Deacon
2019-12-16 11:47 ` Peter Zijlstra
2019-12-16 12:06 ` Arnd Bergmann
2019-12-17 17:07 ` Will Deacon
2019-12-17 18:04 ` Linus Torvalds
2019-12-17 18:05 ` Linus Torvalds
2019-12-17 18:31 ` Will Deacon
2019-12-17 18:32 ` Linus Torvalds
2019-12-18 12:17 ` Michael Ellerman
2019-12-19 12:11 ` Will Deacon
2019-12-18 10:22 ` Christian Borntraeger
2019-12-18 10:35 ` Will Deacon
2019-12-13 12:07 ` Michael Ellerman
2019-12-13 13:53 ` Segher Boessenkool
2019-12-13 21:06 ` Michael Ellerman
2019-12-12 15:10 ` Segher Boessenkool
2019-12-06 22:15 ` [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) pr-tracker-bot
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