Re: Odd looking #PF fault code

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Jarkko,

On 4/3/2022 4:50 PM, Jarkko Sakkinen wrote:
> I get this when trying to get EAUG-EACCEPTCOPY to run on Enarx and I get:
> 

There seems a difference in the error codes described:

> Unexpected PF: address: 0x007f7fff910000, error code 0x15

Error code 0x15 translates to binary 10101 which is:
BIT 0: Present
BIT 2: User
BIT 4: Instruction fetch

> 
> I'm using patches from:
> 
> https://github.com/rchatre/linux/tree/sgx/sgx2_submitted_v2_plus_rwx
> 
> Fault code is in other words PROT|WRITE|USER|RSVD.

PROT|WRITE|USER|RSVD is bits 0,1,2,3 which is 0xF

Did you obtain 0x15 or 0xF as error code?

If EAUG/EACCEPTCOPY was followed by an attempt to execute that page
then 0x15 error could be explained since the page would only support
RW permissions at that time.


> According to arch/x86/kernel/fault.c:
> 
> 	/*
> 	 * Reserved bits are never expected to be set on
> 	 * entries in the user portion of the page tables.
> 	 */
> 	if (unlikely(error_code & X86_PF_RSVD))
> 		pgtable_bad(regs, error_code, address);
> 
> Any clue how this fault code could emit?
> 
> [*] https://github.com/enarx/enarx/pull/1608
> 
> BR, Jarkko


Reinette