linux-kernel - Re: [PATCH v2] x86/fault: Fix wrong signal when vsyscall fails with pkey

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Date:   Mon, 23 Aug 2021 07:55:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jiashuo Liang <liangjs@....edu.cn>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/fault: Fix wrong signal when vsyscall fails with
 pkey

On 7/29/21 8:01 PM, Jiashuo Liang wrote:
> The function __bad_area_nosemaphore() calls kernelmode_fixup_or_oops() with
> parameter "signal" being "pkey", which will send a signal numbered "pkey".
> 
> This bug appears when the kernel fail to access user-given memory pages
> that are protected by pkey, so it can go through the do_user_addr_fault()
> path and pass the !user_mode() check in __bad_area_nosemaphore(). Most
> cases will simply run the kernel fixup code to make an -EFAULT. But when
> another condition current->thread.sig_on_uaccess_err is met, which is
> only used to emulate vsyscall, we will generate the wrong signal.
> 
> A new parameter "pkey" is added to kernelmode_fixup_or_oops() to fix it.
> 
> Fixes: 5042d40a264c ("x86/fault: Bypass no_context() for implicit kernel faults from usermode")
> Signed-off-by: Jiashuo Liang <liangjs@....edu.cn>

This is pretty obscure, only affecting vsyscall emulation, but:

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>