Re: [PATCH 2/2] xtensa: use XCHAL_NUM_AREGS as pt_regs::areg size

Kees Cook
2022-03-07T19:56:46Z

On Sat, Mar 05, 2022 at 10:44:35PM -0800, Max Filippov wrote:
> struct pt_regs is used to access both kernel and user exception frames.
> User exception frames may contain up to XCHAL_NUM_AREG registers that
> task creation and signal delivery code may access, but pt_regs::areg
> array has only 16 entries that cover only the kernel exception frame.
> This results in the following build error:
>
> arch/xtensa/kernel/process.c: In function 'copy_thread':
> arch/xtensa/kernel/process.c:262:52: error: array subscript 53 is above
> array bounds of 'long unsigned int[16]' [-Werror=array-bounds]
> 262 | put_user(regs->areg[caller_ars+1],
>
> Change struct pt_regs::areg size to XCHAL_NUM_AREGS so that it covers
> the whole user exception frame. Adjust task_pt_regs and drop additional
> register copying code from copy_thread now that the whole user exception
> stack frame is copied.
>
> Reported-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
> arch/xtensa/include/asm/ptrace.h | 7 +++----
> arch/xtensa/kernel/process.c | 10 ----------
> 2 files changed, 3 insertions(+), 14 deletions(-)
^^^^^^^^^^^^

Well that's always nice to see in a fix. :) Thanks for digging into
this!

Reviewed-by: Kees Cook <keescook@chromium.org>

--
Kees Cook