> On Feb 3, 2021, at 11:39 AM, Borislav Petkov <[email protected]> wrote:
>
> On Sun, Jan 31, 2021 at 09:24:40AM -0800, Andy Lutomirski wrote:
>> The name no_context() has never been very clear. It's only called for
>> faults from kernel mode, so rename it and change the no-longer-useful
>> user_mode(regs) check to a WARN_ON_ONCE.
>>
>> Cc: Dave Hansen <[email protected]>
>> Cc: Peter Zijlstra <[email protected]>
>> Signed-off-by: Andy Lutomirski <[email protected]>
>> ---
>> arch/x86/mm/fault.c | 28 ++++++++++------------------
>> 1 file changed, 10 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
>> index 177b612c7f33..04cc98ec2423 100644
>> --- a/arch/x86/mm/fault.c
>> +++ b/arch/x86/mm/fault.c
>> @@ -693,17 +693,10 @@ page_fault_oops(struct pt_regs *regs, unsigned long
>> error_code,
>> }
>>
>> static noinline void
>> -no_context(struct pt_regs *regs, unsigned long error_code,
>> - unsigned long address, int signal, int si_code)
>> +kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
>> + unsigned long address, int signal, int si_code)
>
> Ew, I don't like functions with "or" in the name - they're probably not
> doing one thing only as they should.
>
> Why not simply "handle_kernel_fault" ?
Hmm, I could maybe get behind handle_kernelmode_fault. I’ll contemplate it. I
like the name of the function indicating that either it returns after fixing it
or it doesn’t return.
I refuse to say “kernel” without qualification. In this $@!$ file, we have
kernel _mode_, kernel _address_, and kernel _privilege_, and they are all
different.
>
> Also, all the callsites now do:
>
> if (!user_mode(regs)) {
> kernelmode_fixup_or_oops
> ...
>
> I guess you can push the "user_mode" check inside that function for less
> hairy code at the callsites.
I feel like that would be more obfuscated — then the function would return
without fixing anything for usermode faults, return after fixing it for kernel
mode faults, or oops.
>
>> {
>> - 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;
>> - }
>> + WARN_ON_ONCE(user_mode(regs));
>
> I guess...
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
