[v1] riscv: convert bottom half of exception handling to C

[PATCH 2/6] riscv: avoid corrupting the RAS

Posted by Jisheng Zhang 1 year, 6 months ago

Inspired by[1], "modifying the return address of to point to
ret_from_exception will corrupt the RAS", so modify the code
to remove the code of modifying ra.

Link: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/ [1]
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 arch/riscv/kernel/entry.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index c933460ed3e9..81dec627a8d4 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -235,8 +235,8 @@ SYM_CODE_START(ret_from_fork)
 	jalr s0
 1:
 	move a0, sp /* pt_regs */
-	la ra, ret_from_exception
-	tail syscall_exit_to_user_mode
+	call syscall_exit_to_user_mode
+	j ret_from_exception
 SYM_CODE_END(ret_from_fork)
 
 #ifdef CONFIG_IRQ_STACKS
-- 
2.43.0

Re: [PATCH 2/6] riscv: avoid corrupting the RAS

Posted by Cyril Bur 1 year, 5 months ago

On Mon, Jun 17, 2024 at 3:21 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> Inspired by[1], "modifying the return address of to point to
> ret_from_exception will corrupt the RAS", so modify the code
> to remove the code of modifying ra.
>
> Link: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/ [1]
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>

I've run this and it is the same idea that Anton used in the previous patch
Reviewed-by: Cyril Bur <cyrilbur@tenstorrent.com>

> ---
>  arch/riscv/kernel/entry.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index c933460ed3e9..81dec627a8d4 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -235,8 +235,8 @@ SYM_CODE_START(ret_from_fork)
>         jalr s0
>  1:
>         move a0, sp /* pt_regs */
> -       la ra, ret_from_exception
> -       tail syscall_exit_to_user_mode
> +       call syscall_exit_to_user_mode
> +       j ret_from_exception
>  SYM_CODE_END(ret_from_fork)
>
>  #ifdef CONFIG_IRQ_STACKS
> --
> 2.43.0
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv