Re: [PATCH v1 3/5] powerpc/fault: Reorder tests in bad_kernel_fault()

[Nicholas Piggin]

Excerpts from Christophe Leroy's message of August 7, 2020 3:15 am:
> Check address earlier to simplify the following test.

Good logic reduction.

Reviewed-by: Nicholas Piggin 

> Signed-off-by: Christophe Leroy 
> ---
>  arch/powerpc/mm/fault.c | 10 +-
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 9ef9ee244f72..525e0c2b5406 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -210,17 +210,17 @@ 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) &&
> + // Kernel fault on kernel address is bad
> + if (address >= TASK_SIZE)
> + return true;
> +
> + if (!is_exec && (error_code & DSISR_PROTFAULT) &&
>   !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;
> -- 
> 2.25.0
> 
> 

[PATCH v1 3/5] powerpc/fault: Reorder tests in bad_kernel_fault()

[Christophe Leroy]

Check address earlier to simplify the following test.

Signed-off-by: Christophe Leroy 
---
 arch/powerpc/mm/fault.c | 10 +-
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 9ef9ee244f72..525e0c2b5406 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -210,17 +210,17 @@ 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) &&
+   // Kernel fault on kernel address is bad
+   if (address >= TASK_SIZE)
+   return true;
+
+   if (!is_exec && (error_code & DSISR_PROTFAULT) &&
!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;
-- 
2.25.0