linux-kernel - Re: [syzbot] [mm?] BUG: unable to handle kernel paging request in copy_from_kernel

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Date: Thu, 21 Dec 2023 19:59:54 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Thomas Gleixner <tglx@...utronix.de>, bpf <bpf@...r.kernel.org>
Cc: syzbot <syzbot+72aa0161922eba61b50e@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, bp@...en8.de, bp@...e.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, luto@...nel.org, mingo@...hat.com,
 netdev@...r.kernel.org, peterz@...radead.org,
 syzkaller-bugs@...glegroups.com, x86@...nel.org, Jann Horn
 <jannh@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>
Subject: Re: [syzbot] [mm?] BUG: unable to handle kernel paging request in
 copy_from_kernel_nofault

Hi Thomas,

On 12/9/2023 5:01 AM, Thomas Gleixner wrote:
> diff --git a/arch/x86/mm/maccess.c b/arch/x86/mm/maccess.c
> index 6993f026adec..8e846833aa37 100644
> --- a/arch/x86/mm/maccess.c
> +++ b/arch/x86/mm/maccess.c
> @@ -3,6 +3,8 @@
>  #include <linux/uaccess.h>
>  #include <linux/kernel.h>
>  
> +#include <uapi/asm/vsyscall.h>
> +
>  #ifdef CONFIG_X86_64
>  bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
>  {
> @@ -15,6 +17,9 @@ bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
>  	if (vaddr < TASK_SIZE_MAX + PAGE_SIZE)
>  		return false;
>  
> +	if ((vaddr & PAGE_MASK) == VSYSCALL_ADDR)
> +		return false;
> +
>  	/*
>  	 * Allow everything during early boot before 'x86_virt_bits'
>  	 * is initialized.  Needed for instruction decoding in early

Tested-by: Hou Tao <houtao1@...wei.com>

Could you please post a formal patch for the fix ? The patch fixes the
oops when using bpf_probe_read_kernel() or similar bpf helpers [1] to
read from vsyscall address and you can take my tested-by tag if it is
necessary.

[1]:
https://lore.kernel.org/bpf/CABOYnLynjBoFZOf3Z4BhaZkc5hx_kHfsjiW+UWLoB=w33LvScw@mail.gmail.com/