From: Hou Tao <houtao@huaweicloud.com>
To: Sohil Mehta <sohil.mehta@intel.com>, x86@kernel.org, bpf@vger.kernel.org
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, xingwei lee <xrivendell7@gmail.com>,
Jann Horn <jannh@google.com>,
houtao1@huawei.com
Subject: Re: [PATCH bpf 3/3] selftest/bpf: Test the read of vsyscall page under x86-64
Date: Thu, 25 Jan 2024 15:54:21 +0800 [thread overview]
Message-ID: <01ce6947-8b46-9e27-6ce2-ce5763e3c5a9@huaweicloud.com> (raw)
In-Reply-To: <1c260ab1-d4c0-48e6-bf2b-df69bf083d27@intel.com>
On 1/23/2024 8:25 AM, Sohil Mehta wrote:
> On 1/18/2024 11:30 PM, Hou Tao wrote:
>
>> vsyscall page could be disabled by CONFIG_LEGACY_VSYSCALL_NONE or
>> vsyscall=none boot cmd-line, but it doesn't affect the reproduce of the
>> problem and the returned error codes.
>>
> With vsyscall=emulate a direct read of the vsyscall address from
> userspace is expected to go through. This is mode deprecated so maybe it
> wouldn't matter much. Without the fix in patch 2/3, do you see the same
> behavior with vsyscall=emulate set in the cmdline?
Er, I think it depends on whether or not SMAP [1] feature is available.
When SMAP feature is enabled, even the vsyscall page is populated,
reading the vsyscall page through bpf_read_kernel() will trigger a page
fault and then oops. But when there is not SMAP, bpf_read_kernel() will
succeed. So I think the test may need to be skipped if vsyscall_mode is
emulate.
[1]: https://en.wikipedia.org/wiki/Supervisor_Mode_Access_Prevention
>
> Sohil
prev parent reply other threads:[~2024-01-25 7:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-19 7:30 [PATCH bpf 0/3] Fix the read of vsyscall page through bpf Hou Tao
2024-01-19 7:30 ` [PATCH bpf 1/3] x86/mm: Move is_vsyscall_vaddr() into mm_internal.h Hou Tao
2024-01-20 0:35 ` Sohil Mehta
2024-01-20 1:29 ` Hou Tao
2024-01-19 7:30 ` [PATCH bpf 2/3] x86/mm: Disallow vsyscall page read for copy_from_kernel_nofault() Hou Tao
2024-01-23 0:18 ` Sohil Mehta
2024-01-25 7:18 ` Hou Tao
2024-01-19 7:30 ` [PATCH bpf 3/3] selftest/bpf: Test the read of vsyscall page under x86-64 Hou Tao
2024-01-22 6:30 ` Yonghong Song
2024-01-25 6:37 ` Hou Tao
2024-01-23 0:25 ` Sohil Mehta
2024-01-25 7:54 ` Hou Tao [this message]
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