Christophe Leroy <christophe.le...@csgroup.eu> writes:
> 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>
> Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> ---
> v3: rebased
> v2: Squashed with the preceeding patch which was re-ordering tests that get
> removed in this patch.
> ---
> arch/powerpc/mm/fault.c | 23 +++++++----------------
> 1 file changed, 7 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 3fcd34c28e10..1770b41e4730 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -210,28 +210,19 @@ static bool bad_kernel_fault(struct pt_regs *regs,
> unsigned long error_code,
> return true;
> }
>
> - if (!is_exec && address < TASK_SIZE && (error_code & (DSISR_PROTFAULT |
> DSISR_KEYFAULT)) &&
> - !search_exception_tables(regs->nip)) {
> - pr_crit_ratelimited("Kernel attempted to access user page (%lx)
> - exploit attempt? (uid: %d)\n",
> - address,
> - from_kuid(&init_user_ns, current_uid()));
> - }
> -
> // Kernel fault on kernel address is bad
> if (address >= TASK_SIZE)
> return true;
>
> - // 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))
> + // 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 %s user page (%lx) -
> exploit attempt? (uid: %d)\n",
> + is_write ? "write" : "read", address,
> + from_kuid(&init_user_ns, current_uid()));
> return true;
> + }
With this I am wondering whether the WARN() in bad_kuap_fault() is
needed. A direct access of userspace address will trigger this, whereas
previously we used bad_kuap_fault() only to identify incorrect restore
of AMR register (ie, to identify kernel bugs). Hence a WARN() there was
useful. We loose that differentiation now?
>
> - // 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
