Re: [syzbot] [mm?] BUG: unable to handle kernel paging request in copy_from_kernel_nofault

From: Hou Tao <houtao@huaweicloud.com>
To: Thomas Gleixner <tglx@linutronix.de>, bpf <bpf@vger.kernel.org>
Cc: syzbot <syzbot+72aa0161922eba61b50e@syzkaller.appspotmail.com>,
	akpm@linux-foundation.org, bp@alien8.de, bp@suse.de,
	dave.hansen@linux.intel.com, hpa@zytor.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	luto@kernel.org, mingo@redhat.com, netdev@vger.kernel.org,
	peterz@infradead.org, syzkaller-bugs@googlegroups.com,
	x86@kernel.org, Jann Horn <jannh@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	John Fastabend <john.fastabend@gmail.com>
Subject: Re: [syzbot] [mm?] BUG: unable to handle kernel paging request in copy_from_kernel_nofault
Date: Thu, 21 Dec 2023 19:59:54 +0800	[thread overview]
Message-ID: <e24b125c-8ff4-9031-6c53-67ff2e01f316@huaweicloud.com> (raw)
In-Reply-To: <87r0jwquhv.ffs@tglx>

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@huawei.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/