linux-kernel - Re: [PATCH 07/11] x86/fault: Split the OOPS code out from no

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Message-ID: <20210203185517.GH13819@zn.tnic>
Date:   Wed, 3 Feb 2021 19:56:25 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 07/11] x86/fault: Split the OOPS code out from
 no_context()

On Sun, Jan 31, 2021 at 09:24:38AM -0800, Andy Lutomirski wrote:
> Not all callers of no_context() want to run exception fixups.
> Separate the OOPS code out from the fixup code in no_context().
> 
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/mm/fault.c | 116 +++++++++++++++++++++++---------------------
>  1 file changed, 62 insertions(+), 54 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 1939e546beae..6f43d080e1e8 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -618,53 +618,20 @@ static void set_signal_archinfo(unsigned long address,
>  }
>  
>  static noinline void
> -no_context(struct pt_regs *regs, unsigned long error_code,
> -	   unsigned long address, int signal, int si_code)
> +page_fault_oops(struct pt_regs *regs, unsigned long error_code,

Not sure about this name - it still tries to recover:
efi_recover_from_page_fault().

Judging by where it is called, maybe no_context_tail() or
no_context_oops() or no_context_finish_me_already()...

Yah, I haz no better idea. :-\

...

> @@ -739,6 +692,61 @@ no_context(struct pt_regs *regs, unsigned long error_code,
>  	oops_end(flags, regs, sig);
>  }
>  
> +static noinline void
> +no_context(struct pt_regs *regs, unsigned long error_code,
> +	   unsigned long address, int signal, int si_code)
> +{
> +	if (user_mode(regs)) {
> +		/*
> +		 * This is an implicit supervisor-mode access from user
> +		 * mode.  Bypass all the kernel-mode recovery code and just
> +		 * OOPS.
> +		 */
> +		goto oops;

Just do

		return page_fault_oops(...);

here and get rid of the label.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette