Re: [PATCH 08/20] signal/sparc: In setup_tsb_params convert open coded BUG into BUG

Kees Cook
2021-10-21T16:12:52Z

On Wed, Oct 20, 2021 at 12:43:54PM -0500, Eric W. Biederman wrote:
> The function setup_tsb_params has exactly one caller tsb_grow. The
> function tsb_grow passes in a tsb_bytes value that is between 8192 and
> 1048576 inclusive, and is guaranteed to be a power of 2. The function
> setup_tsb_params verifies this property with a switch statement and
> then prints an error and causes the task to exit if this is not true.
>
> In practice that print statement can never be reached because tsb_grow
> never passes in a bad tsb_size. So if tsb_size ever gets a bad value
> that is a kernel bug.
>
> So replace the do_exit which is effectively an open coded version of
> BUG() with an actuall call to BUG(). Making it clearer that this
> is a case that can never, and should never happen.
>
> Cc: David Miller <davem@davemloft.net>
> Cc: sparclinux@vger.kernel.org
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> arch/sparc/mm/tsb.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/sparc/mm/tsb.c b/arch/sparc/mm/tsb.c
> index 0dce4b7ff73e..912205787161 100644
> --- a/arch/sparc/mm/tsb.c
> +++ b/arch/sparc/mm/tsb.c
> @@ -266,7 +266,7 @@ static void setup_tsb_params(struct mm_struct *mm, unsigned long tsb_idx, unsign
> default:
> printk(KERN_ERR "TSB[%s:%d]: Impossible TSB size %lu, killing process.\n",
> current->comm, current->pid, tsb_bytes);
> - do_exit(SIGSEGV);
> + BUG();
> }
> tte |= pte_sz_bits(page_sz);

Given the other uses of BUG() here, this seems okay.

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

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Kees Cook