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SubjectRe: [PATCH v6 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state
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@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).

--
Catalin

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