* Andy Lutomirski <l...@kernel.org> wrote:
> The fault handling code tries to validate that a page fault from
> user mode that would extend the stack is within a certain range of
> the user SP. regs->sp is only equal to the user SP if
> user_mode(regs). In the extremely unlikely event that that
> sw_error_code had the USER bit set but the faulting instruction was
> in the kernel (i.e. the faulting instruction was WRUSS), then the
> *kernel* stack pointer would have been checked, which would be an
> info leak.
>
> Note to -stable maintainers: don't backport this unless you backport
> CET. The bug it fixes is unobservable in current kernels.
>
> Signed-off-by: Andy Lutomirski <l...@kernel.org>
> ---
> arch/x86/mm/fault.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 91d4d2722f2e..eae7ee3ce89b 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
> bad_area(regs, sw_error_code, address);
> return;
> }
> - if (sw_error_code & X86_PF_USER) {
> + if (user_mode(regs)) {
> /*
> * Accessing the stack below %sp is always a bug.
> * The large cushion allows instructions like enter
Note that this check is gone now due to:
1d8ca3be86eb: x86/mm/fault: Allow stack access below %rsp
Thanks,
Ingo
