Re: [PATCH 2/4] x86: Fix the hw_breakpoint range check

Borislav Petkov
2013-11-24T13:40:57Z

On Sun, Nov 24, 2013 at 11:32:49AM +0100, Frederic Weisbecker wrote:
> From: Oleg Nesterov <oleg@redhat.com>
>
> arch_check_bp_in_kernelspace() tries to avoid the overflow and does 2
> TASK_SIZE checks but it needs OR, not AND. Consider va = TASK_SIZE -1
> and len = 2 case.
>
> Note: TASK_SIZE doesn't look right at least on x86, I think it should
> be replaced by TASK_SIZE_MAX.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Fixes: 0067f1297241ea567f2b22a455519752d70fcca9
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> ---
> arch/x86/kernel/hw_breakpoint.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
> index f66ff16..1131c1f 100644
> --- a/arch/x86/kernel/hw_breakpoint.c
> +++ b/arch/x86/kernel/hw_breakpoint.c
> @@ -200,7 +200,7 @@ int arch_check_bp_in_kernelspace(struct perf_event *bp)
> va = info->address;
> len = get_hbp_len(info->len);
>
> - return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
> + return (va >= TASK_SIZE) || ((va + len - 1) >= TASK_SIZE);

Well, can't you simplify it even further?

return (va + len - 1) >= TASK_SIZE;

AFAICT, the high end of the range matters, no?

Unless the original code was meant to short-circuit at the first
comparison already...

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--