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Date: Wed, 28 Jun 2017 14:15:18 +0300
From: Andrey Ryabinin <aryabinin@...tuozzo.com>
To: Dmitry Vyukov <dvyukov@...gle.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will.deacon@....com>,
"H. Peter Anvin" <hpa@...or.com>,
kasan-dev <kasan-dev@...glegroups.com>,
"x86@...nel.org" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] locking/atomics: don't alias ____ptr
On 06/28/2017 01:16 PM, Dmitry Vyukov wrote:
> On Wed, Jun 28, 2017 at 12:02 PM, Sebastian Andrzej Siewior
> <bigeasy@...utronix.de> wrote:
>> Trying to boot tip/master resulted in:
>> |DMAR: dmar0: Using Queued invalidation
>> |DMAR: dmar1: Using Queued invalidation
>> |DMAR: Setting RMRR:
>> |DMAR: Setting identity map for device 0000:00:1a.0 [0xbdcf9000 - 0xbdd1dfff]
>> |BUG: unable to handle kernel NULL pointer dereference at (null)
>> |IP: __domain_mapping+0x10f/0x3d0
>> |PGD 0
>> |P4D 0
>> |
>> |Oops: 0002 [#1] PREEMPT SMP
>> |Modules linked in:
>> |CPU: 19 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc6-00117-g235a93822a21 #113
>> |task: ffff8805271c2c80 task.stack: ffffc90000058000
>> |RIP: 0010:__domain_mapping+0x10f/0x3d0
>> |RSP: 0000:ffffc9000005bca0 EFLAGS: 00010246
>> |RAX: 0000000000000000 RBX: 00000000bdcf9003 RCX: 0000000000000000
>> |RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000001
>> |RBP: ffffc9000005bd00 R08: ffff880a243e9780 R09: ffff8805259e67c8
>> |R10: 00000000000bdcf9 R11: 0000000000000000 R12: 0000000000000025
>> |R13: 0000000000000025 R14: 0000000000000000 R15: 00000000000bdcf9
>> |FS: 0000000000000000(0000) GS:ffff88052acc0000(0000) knlGS:0000000000000000
>> |CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> |CR2: 0000000000000000 CR3: 0000000001c0f000 CR4: 00000000000406e0
>> |Call Trace:
>> | iommu_domain_identity_map+0x5a/0x80
>> | domain_prepare_identity_map+0x9f/0x160
>> | iommu_prepare_identity_map+0x7e/0x9b
>>
>> bisect points to commit 235a93822a21 ("locking/atomics, asm-generic: Add KASAN
>> instrumentation to atomic operations"), RIP is at
>> tmp = cmpxchg64_local(&pte->val, 0ULL, pteval);
>> in drivers/iommu/intel-iommu.c. The assembly for this inline assembly
>> is:
>> xor %edx,%edx
>> xor %eax,%eax
>> cmpxchg %rbx,(%rdx)
>>
>> and as you see edx is set to zero and used later as a pointer via the
>> full register. This happens with gcc-6, 5 and 8 (snapshot from last
>> week).
>> After a longer while of searching and swearing I figured out that this
>> bug occures once cmpxchg64_local() and cmpxchg_local() uses the same
>> ____ptr macro and they are shadow somehow. What I don't know why edx is
>> set to zero.
>>
>> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
>> ---
>> include/asm-generic/atomic-instrumented.h | 12 ++++++------
>> 1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h
>> index a0f5b7525bb2..ac6155362b39 100644
>> --- a/include/asm-generic/atomic-instrumented.h
>> +++ b/include/asm-generic/atomic-instrumented.h
>> @@ -359,16 +359,16 @@ static __always_inline bool atomic64_add_negative(s64 i, atomic64_t *v)
>>
>> #define cmpxchg64(ptr, old, new) \
>> ({ \
>> - __typeof__(ptr) ____ptr = (ptr); \
>> - kasan_check_write(____ptr, sizeof(*____ptr)); \
>> - arch_cmpxchg64(____ptr, (old), (new)); \
>> + __typeof__(ptr) ____ptr64 = (ptr); \
>> + kasan_check_write(____ptr64, sizeof(*____ptr64));\
>> + arch_cmpxchg64(____ptr64, (old), (new)); \
>> })
>>
>> #define cmpxchg64_local(ptr, old, new) \
>> ({ \
>> - __typeof__(ptr) ____ptr = (ptr); \
>> - kasan_check_write(____ptr, sizeof(*____ptr)); \
>> - arch_cmpxchg64_local(____ptr, (old), (new)); \
>> + __typeof__(ptr) ____ptr64 = (ptr); \
>> + kasan_check_write(____ptr64, sizeof(*____ptr64));\
>> + arch_cmpxchg64_local(____ptr64, (old), (new)); \
>> })
>>
>> #define cmpxchg_double(p1, p2, o1, o2, n1, n2) \
>
>
> Doh! Thanks for fixing this. I think I've a similar crash in a
> different place when I developed the patch.
> The problem is that when we do:
>
> __typeof__(ptr) ____ptr = (ptr); \
> arch_cmpxchg64_local(____ptr, (old), (new)); \
>
> We don't necessary pass value of our just declared ____ptr to
> arch_cmpxchg64_local(). We just pass a symbolic identifier. So if
> arch_cmpxchg64_local() declares own ____ptr and then tries to use what
> we passed ("____ptr") it will actually refer to own variable declared
> rather than to what we wanted to pass in.
>
> In my case I ended up with something like:
>
> __typeof__(foo) __ptr = __ptr;
>
> which compiler decided to turn into 0.
>
> Thank you, macros.
>
> We can add more underscores, but the problem can happen again. Should
> we prefix current function/macro name to all local vars?..
>
The main problem here is that arch_cmpxchg64_local() calls cmpxhg_local() instead of using arch_cmpxchg_local().
So, the patch bellow should fix the problem, also this will fix double instrumentation of cmpcxchg64[_local]().
But I haven't tested this patch yet.
---
arch/x86/include/asm/cmpxchg_64.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index fafaebacca2d..7046a3cc2493 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -9,13 +9,13 @@ static inline void set_64bit(volatile u64 *ptr, u64 val)
#define arch_cmpxchg64(ptr, o, n) \
({ \
BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- cmpxchg((ptr), (o), (n)); \
+ arch_cmpxchg((ptr), (o), (n)); \
})
#define arch_cmpxchg64_local(ptr, o, n) \
({ \
BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- cmpxchg_local((ptr), (o), (n)); \
+ arch_cmpxchg_local((ptr), (o), (n)); \
})
#define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX16)
--
2.13.0
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