linux-kernel - Re: [patch V3 02/13] entry: Provide generic syscall exit function

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Date:   Thu, 16 Jul 2020 13:55:11 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        linux-arch@...r.kernel.org, Will Deacon <will@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Keno Fischer <keno@...iacomputing.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [patch V3 02/13] entry: Provide generic syscall exit function

On Thu, Jul 16, 2020 at 08:22:10PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Like syscall entry all architectures have similar and pointlessly different
> code to handle pending work before returning from a syscall to user space.
> 
>   1) One-time syscall exit work:
>       - rseq syscall exit
>       - audit
>       - syscall tracing
>       - tracehook (single stepping)
> 
>   2) Preparatory work
>       - Exit to user mode loop (common TIF handling).
>       - Architecture specific one time work arch_exit_to_user_mode_prepare()
>       - Address limit and lockdep checks
>      
>   3) Final transition (lockdep, tracing, context tracking, RCU). Invokes
>      arch_exit_to_user_mode() to handle e.g. speculation mitigations
> 
> Provide a generic version based on the x86 code which has all the RCU and
> instrumentation protections right.
> 
> Provide a variant for interrupt return to user mode as well which shares
> the above #2 and #3 work items.
> 
> After syscall_exit_to_user_mode() and irqentry_exit_to_user_mode() the
> architecture code just has to return to user space. The code after
> returning from these functions must not be instrumented.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

This looks correct to me. Did you happen to run the seccomp selftests
under this series?

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook