Re: [PATCH v5 1/4] syscalls: Restore address limit after a syscall

[Thomas Garnier]

On Thu, Mar 23, 2017 at 1:15 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Thu, Mar 23, 2017 at 10:25 AM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
>> This patch ensures a syscall does not return to user-mode with a kernel
>> address limit. If that happened, a process can corrupt kernel-mode
>> memory and elevate privileges.
>>
>> For example, it would mitigation this bug:
>>
>> - https://bugs.chromium.org/p/project-zero/issues/detail?id=990
>>
>> The CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE option is also
>> added so each architecture can optimize this change.
>>
>> Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
>
> Awesome. :) I've tested this on x86 and arm with the LKDTM patch I'll
> post in a moment.
>
> [   46.977823] lkdtm: Performing direct entry CORRUPT_USER_DS
> [   46.978966] lkdtm: setting bad task size limit
> [   46.980302] ------------[ cut here ]------------
> [   46.981219] kernel BUG at ./include/linux/syscalls.h:200!
>
> Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks Kees. Any additional feedback? Andy?

>
> (Also note, your Signed-off-by lines are missing in patches 2-4)
>
> --
> Kees Cook
> Pixel Security



-- 
Thomas