Excerpts from Christophe Leroy's message of August 7, 2020 3:15 am:
> search_exception_tables() is an heavy operation, we have to avoid it.
> When KUAP is selected, we'll know the fault has been blocked by KUAP.
> Otherwise, it behaves just as if the address was already in the TLBs
> and no fault was generated.
>
> Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
Sorry I missed reviewing this. Yes, we discussed this and decided
that it's not effective I think (and KUAP solves it properly).
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> ---
> arch/powerpc/mm/fault.c | 20 +++++---------------
> 1 file changed, 5 insertions(+), 15 deletions(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 525e0c2b5406..edde169ba3a6 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -214,24 +214,14 @@ static bool bad_kernel_fault(struct pt_regs *regs,
> unsigned long error_code,
> if (address >= TASK_SIZE)
> return true;
>
> - if (!is_exec && (error_code & DSISR_PROTFAULT) &&
> - !search_exception_tables(regs->nip)) {
> + // Read/write fault blocked by KUAP is bad, it can never succeed.
> + if (bad_kuap_fault(regs, address, is_write)) {
> pr_crit_ratelimited("Kernel attempted to access user page (%lx)
> - exploit attempt? (uid: %d)\n",
> - address,
> - from_kuid(&init_user_ns, current_uid()));
> - }
> -
> - // Fault on user outside of certain regions (eg. copy_tofrom_user()) is
> bad
> - if (!search_exception_tables(regs->nip))
> - return true;
> -
> - // Read/write fault in a valid region (the exception table search passed
> - // above), but blocked by KUAP is bad, it can never succeed.
> - if (bad_kuap_fault(regs, address, is_write))
> + address, from_kuid(&init_user_ns,
> current_uid()));
> return true;
> + }
>
> - // What's left? Kernel fault on user in well defined regions (extable
> - // matched), and allowed by KUAP in the faulting context.
> + // What's left? Kernel fault on user and allowed by KUAP in the
> faulting context.
> return false;
> }
>
> --
> 2.25.0
>
>
