linux-kernel - Re: [PATCH v2] mm: Fix possible NULL pointer dereference in __swap

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Message-ID: <8bda689f466f7426df696ec52648592f262091bb@linux.dev>
Date: Sat, 15 Feb 2025 08:24:07 +0000
From: "Yosry Ahmed" <yosry.ahmed@...ux.dev>
To: "gaoxu" <gaoxu2@...or.com>, "Andrew Morton" <akpm@...ux-foundation.org>,
 linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, "Suren  Baghdasaryan" <surenb@...gle.com>,
 "Barry Song" <21cnbao@...il.com>, "yipengxiang" <yipengxiang@...or.com>
Subject: Re: [PATCH v2] mm: Fix possible NULL pointer dereference in
 __swap_duplicate

February 14, 2025 at 10:52 PM, "gaoxu" <gaoxu2@...or.com> wrote:



> 
> Add a NULL check on the return value of swp_swap_info in __swap_duplicate
> 
> to prevent crashes caused by NULL pointer dereference.
> 
> The reason why swp_swap_info() returns NULL is unclear; it may be due to
> 
> CPU cache issues or DDR bit flips. The probability of this issue is very
> 
> small, and the stack info we encountered is as follows：
> 
> Unable to handle kernel NULL pointer dereference at virtual address
> 
> 0000000000000058
> 
> [RB/E]rb_sreason_str_set: sreason_str set null_pointer
> 
> Mem abort info:
> 
>  ESR = 0x0000000096000005
> 
>  EC = 0x25: DABT (current EL), IL = 32 bits
> 
>  SET = 0, FnV = 0
> 
>  EA = 0, S1PTW = 0
> 
>  FSC = 0x05: level 1 translation fault
> 
> Data abort info:
> 
>  ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
> 
>  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> 
>  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> 
> user pgtable: 4k pages, 39-bit VAs, pgdp=00000008a80e5000
> 
> [0000000000000058] pgd=0000000000000000, p4d=0000000000000000,
> 
> pud=0000000000000000
> 
> Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
> 
> Skip md ftrace buffer dump for: 0x1609e0
> 
> ...
> 
> pc : swap_duplicate+0x44/0x164
> 
> lr : copy_page_range+0x508/0x1e78
> 
> sp : ffffffc0f2a699e0
> 
> x29: ffffffc0f2a699e0 x28: ffffff8a5b28d388 x27: ffffff8b06603388
> 
> x26: ffffffdf7291fe70 x25: 0000000000000006 x24: 0000000000100073
> 
> x23: 00000000002d2d2f x22: 0000000000000008 x21: 0000000000000000
> 
> x20: 00000000002d2d2f x19: 18000000002d2d2f x18: ffffffdf726faec0
> 
> x17: 0000000000000000 x16: 0010000000000001 x15: 0040000000000001
> 
> x14: 0400000000000001 x13: ff7ffffffffffb7f x12: ffeffffffffffbff
> 
> x11: ffffff8a5c7e1898 x10: 0000000000000018 x9 : 0000000000000006
> 
> x8 : 1800000000000000 x7 : 0000000000000000 x6 : ffffff8057c01f10
> 
> x5 : 000000000000a318 x4 : 0000000000000000 x3 : 0000000000000000
> 
> x2 : 0000006daf200000 x1 : 0000000000000001 x0 : 18000000002d2d2f
> 
> Call trace:
> 
>  swap_duplicate+0x44/0x164
> 
>  copy_page_range+0x508/0x1e78
> 
>  copy_process+0x1278/0x21cc
> 
>  kernel_clone+0x90/0x438
> 
>  __arm64_sys_clone+0x5c/0x8c
> 
>  invoke_syscall+0x58/0x110
> 
>  do_el0_svc+0x8c/0xe0
> 
>  el0_svc+0x38/0x9c
> 
>  el0t_64_sync_handler+0x44/0xec
> 
>  el0t_64_sync+0x1a8/0x1ac
> 
> Code: 9139c35a 71006f3f 54000568 f8797b55 (f9402ea8)
> 
> ---[ end trace 0000000000000000 ]---
> 
> Kernel panic - not syncing: Oops: Fatal exception
> 
> SMP: stopping secondary CPUs
> 
> The patch seems to only provide a workaround, but there are no more
> 
> effective software solutions to handle the bit flips problem. This path
> 
> will change the issue from a system crash to a process exception, thereby
> 
> reducing the impact on the entire machine.
> 
> Signed-off-by: gaoxu <gaoxu2@...or.com>
> 
> Reviewed-by: Yosry Ahmed <yosry.ahmed@...ux.dev>


I did not review this patch, I only made a suggestion. Please only add Review tags when explicitly given.