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Message-ID: <CAADnVQK8avOCKuqE2g__WOKzTKCAqdphxjncvXuEQ801g8jf-g@mail.gmail.com>
Date: Wed, 14 Feb 2024 14:51:51 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Sohil Mehta <sohil.mehta@...el.com>, Thomas Gleixner <tglx@...utronix.de>
Cc: Hou Tao <houtao@...weicloud.com>, X86 ML <x86@...nel.org>, bpf <bpf@...r.kernel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H . Peter Anvin" <hpa@...or.com>, LKML <linux-kernel@...r.kernel.org>,
xingwei lee <xrivendell7@...il.com>, Jann Horn <jannh@...gle.com>,
Yonghong Song <yonghong.song@...ux.dev>, Hou Tao <houtao1@...wei.com>
Subject: Re: [PATCH bpf v3 2/3] x86/mm: Disallow vsyscall page read for copy_from_kernel_nofault()
On Fri, Feb 2, 2024 at 11:03 AM Sohil Mehta <sohil.mehta@...el.com> wrote:
>
> On 2/2/2024 2:39 AM, Hou Tao wrote:
> > From: Hou Tao <houtao1@...wei.com>
> >
> > When trying to use copy_from_kernel_nofault() to read vsyscall page
> > through a bpf program, the following oops was reported:
> >
> > BUG: unable to handle page fault for address: ffffffffff600000
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > PGD 3231067 P4D 3231067 PUD 3233067 PMD 3235067 PTE 0
> > Oops: 0000 [#1] PREEMPT SMP PTI
> > CPU: 1 PID: 20390 Comm: test_progs ...... 6.7.0+ #58
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ......
> > RIP: 0010:copy_from_kernel_nofault+0x6f/0x110
> > ......
> > Call Trace:
> > <TASK>
> > ? copy_from_kernel_nofault+0x6f/0x110
> > bpf_probe_read_kernel+0x1d/0x50
> > bpf_prog_2061065e56845f08_do_probe_read+0x51/0x8d
> > trace_call_bpf+0xc5/0x1c0
> > perf_call_bpf_enter.isra.0+0x69/0xb0
> > perf_syscall_enter+0x13e/0x200
> > syscall_trace_enter+0x188/0x1c0
> > do_syscall_64+0xb5/0xe0
> > entry_SYSCALL_64_after_hwframe+0x6e/0x76
> > </TASK>
> > ......
> > ---[ end trace 0000000000000000 ]---
> >
> > The oops is triggered when:
> >
> > 1) A bpf program uses bpf_probe_read_kernel() to read from the vsyscall
> > page and invokes copy_from_kernel_nofault() which in turn calls
> > __get_user_asm().
> >
> > 2) Because the vsyscall page address is not readable from kernel space,
> > a page fault exception is triggered accordingly.
> >
> > 3) handle_page_fault() considers the vsyscall page address as a user
> > space address instead of a kernel space address. This results in the
> > fix-up setup by bpf not being applied and a page_fault_oops() is invoked
> > due to SMAP.
> >
> > Considering handle_page_fault() has already considered the vsyscall page
> > address as a userspace address, fix the problem by disallowing vsyscall
> > page read for copy_from_kernel_nofault().
> >
> > Originally-by: Thomas Gleixner <tglx@...utronix.de>
Thomas,
could you please Ack the patch if you're still ok with it,
so we can take through the bpf tree to Linus soon ?
Not only syzbot, but real users are hitting this bug.
Thanks!
> > Reported-by: syzbot+72aa0161922eba61b50e@...kaller.appspotmail.com
> > Closes: https://lore.kernel.org/bpf/CAG48ez06TZft=ATH1qh2c5mpS5BT8UakwNkzi6nvK5_djC-4Nw@mail.gmail.com
> > Reported-by: xingwei lee <xrivendell7@...il.com>
> > Closes: https://lore.kernel.org/bpf/CABOYnLynjBoFZOf3Z4BhaZkc5hx_kHfsjiW+UWLoB=w33LvScw@mail.gmail.com
> > Signed-off-by: Hou Tao <houtao1@...wei.com>
> > ---
> > arch/x86/mm/maccess.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
>
> Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>
>
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