Re: [PATCH 07/11] x86/fault: Split the OOPS code out from no_context()

From: Andy Lutomirski <luto@amacapital.net>
To: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>,
	x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Yonghong Song <yhs@fb.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 07/11] x86/fault: Split the OOPS code out from no_context()
Date: Wed, 3 Feb 2021 11:29:39 -0800	[thread overview]
Message-ID: <78B808CF-16E2-4C41-B680-0AFD1428ED4A@amacapital.net> (raw)
In-Reply-To: <20210203185517.GH13819@zn.tnic>

> On Feb 3, 2021, at 10:56 AM, Borislav Petkov <bp@alien8.de> wrote:
> 
> 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@linux.intel.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Signed-off-by: Andy Lutomirski <luto@kernel.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().
> 

That function is a lie. It tries to keep the system alive but it doesn’t return if it “recovers”.   Maybe I should add a comment?

> 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