Re: [PATCH v4 10/17] x86/entry/64: Really create an error-entry-from-usermode code path

Andy Lutomirski
2015-07-02T15:33:35Z

On Thu, Jul 2, 2015 at 3:25 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Mon, Jun 29, 2015 at 12:33:42PM -0700, Andy Lutomirski wrote:
>> In 539f51136500 ("x86/asm/entry/64: Disentangle error_entry/exit
>> gsbase/ebx/usermode code"), I arranged the code slightly wrong --
>> IRET faults would skip the code path that was intended to execute on
>> all error entries from user mode. Fix it up.
>>
>> This does not fix a bug, but we'll need it, and it slightly shrinks
>> the code.
>>
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>> arch/x86/entry/entry_64.S | 12 ++++++++----
>> 1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> index 141a5d49dddc..cd9cbc62159c 100644
>> --- a/arch/x86/entry/entry_64.S
>> +++ b/arch/x86/entry/entry_64.S
>> @@ -1145,9 +1145,14 @@ ENTRY(error_entry)
>> testb $3, CS+8(%rsp)
>> jz error_kernelspace
>>
>> - /* We entered from user mode */
>> +error_entry_from_usermode_swapgs:
>> + /*
>> + * We entered from user mode or we're pretending to have entered
>> + * from user mode due to an IRET fault.
>> + */
>> SWAPGS
>>
>> +error_entry_from_usermode_after_swapgs:
>> error_entry_done:
>
> Why the second label?

"Migrate error and interrupt exit work to C" puts code between those
labels. I could squash the patches together to make it less
mysterious.

>
> Also, please make all those labels local by prefixing them with .L
> because they appear unnecesasrily in objdump output as global symbols.

Will do.

>
> $ objdump -d vmlinux | grep -E "^[0-9a-f]+ <(error_entry_\w*|error_kernelspace|bstep_iret|error_bad_iret)"
> ffffffff8167a4a8 <error_entry_from_usermode_swapgs>:
> ffffffff8167a4ab <error_entry_done>:
> ffffffff8167a4b1 <error_kernelspace>:
> ffffffff8167a4e0 <bstep_iret>:
> ffffffff8167a4e8 <error_bad_iret>:
>
> Oh, and shorter please :)
>

I'll try to think of a good shorter name. No promises :)

--Andy