[PATCH v6 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state
thgarnie at google.com
Wed Apr 5 11:14:34 PDT 2017
On Wed, Apr 5, 2017 at 10:49 AM, Catalin Marinas
<catalin.marinas at arm.com> wrote:
> On Wed, Apr 05, 2017 at 07:36:17AM -0700, Thomas Garnier wrote:
>> On Wed, Apr 5, 2017 at 7:22 AM, Catalin Marinas <catalin.marinas at arm.com> wrote:
>> > On Tue, Apr 04, 2017 at 10:47:27AM -0700, Thomas Garnier wrote:
>> >> +
>> >> ldr x1, [tsk, #TSK_TI_FLAGS]
>> >> and x2, x1, #_TIF_WORK_MASK
>> >> cbnz x2, work_pending
>> >> @@ -779,6 +788,12 @@ finish_ret_to_user:
>> >> kernel_exit 0
>> >> ENDPROC(ret_to_user)
>> >> +addr_limit_fail:
>> >> + stp x0, lr, [sp,#-16]!
>> >> + bl asm_verify_pre_usermode_state
>> >> + ldp x0, lr, [sp],#16
>> >> + ret lr
>> > Where is this supposed to return? What is the value of lr when branching
>> > to addr_limit_fail?
>> It is not supposed to return. Do you think I should remove stp, ldp,
>> ret and jut add a brk 0x100 or jmp/call a break/bug function?
> Can you not just make addr_limit_fail a C function which never returns
> (similar to what we to with bad_mode() on arm64)? Since addr_limit_fail
> is only called when the segment is not the right one, I don't really see
> why you need another call to asm_verify_pre_usermode_state() to do a
> similar check again. Just panic in addr_limit_fail (unless I
> misunderstood what you are trying to achieve).
Calling asm_verify_pre_usermode_state has the advantage of having a
clear BUG_ON for the error (versus a panic description).
What do you think about replacing asm_verify_pre_usermode_state by a
"address_limit_fail" function that still calls
verify_pre_usermode_state but panic afterwards (because it should
The assembly code would be easier to understand and in case of error
the BUG_ON is clear for the user.
More information about the linux-arm-kernel