From: Björn Töpel <[email protected]>
The RISC-V calling convention passes the first argument, and the
return value in the a0 register. For this reason, the a0 register
needs some extra care; When handling syscalls, the a0 register is
saved into regs->orig_a0, so a0 can be properly restored for,
e.g. interrupted syscalls.
This functionality was broken with the introduction of the generic
entry patches. Here, a0 was saved into orig_a0 after calling
syscall_enter_from_user_mode(), which can change regs->a0 for some
paths, incorrectly restoring a0.
This is resolved, by saving a0 prior doing the
syscall_enter_from_user_mode() call.
Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reviewed-by: Heiko Stuebner <[email protected]>
Tested-by: Heiko Stuebner <[email protected]>
Signed-off-by: Björn Töpel <[email protected]>
---
arch/riscv/kernel/traps.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 1f4e37be7eb3..8c258b78c925 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -270,11 +270,11 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
if (user_mode(regs)) {
ulong syscall = regs->a7;
- syscall = syscall_enter_from_user_mode(regs, syscall);
-
regs->epc += 4;
regs->orig_a0 = regs->a0;
+ syscall = syscall_enter_from_user_mode(regs, syscall);
+
if (syscall < NR_syscalls)
syscall_handler(regs, syscall);
else
base-commit: d34a6b715a23ccd9c9d0bc7a475bea59dc3e28b2
--
2.37.2
On Mon, Apr 03, 2023 at 08:52:07AM +0200, Bj?rn T?pel wrote:
> From: Bj?rn T?pel <[email protected]>
>
> The RISC-V calling convention passes the first argument, and the
> return value in the a0 register. For this reason, the a0 register
> needs some extra care; When handling syscalls, the a0 register is
> saved into regs->orig_a0, so a0 can be properly restored for,
> e.g. interrupted syscalls.
>
> This functionality was broken with the introduction of the generic
> entry patches. Here, a0 was saved into orig_a0 after calling
> syscall_enter_from_user_mode(), which can change regs->a0 for some
> paths, incorrectly restoring a0.
>
> This is resolved, by saving a0 prior doing the
> syscall_enter_from_user_mode() call.
>
> Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
> Reviewed-by: Heiko Stuebner <[email protected]>
> Tested-by: Heiko Stuebner <[email protected]>
> Signed-off-by: Bj?rn T?pel <[email protected]>
As you pointed out, v12 did indeed have this ordering, so *deep breath*
Reported-by: Conor Dooley <[email protected]>
Link: https://lore.kernel.org/linux-riscv/60ee7c26-1a70-427d-beaf-92e2989fc479@spud/
Reviewed-by: Conor Dooley <[email protected]>
Tested-by: Conor Dooley <[email protected]>
Thanks for fixing this Bj?rn!
> ---
> arch/riscv/kernel/traps.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 1f4e37be7eb3..8c258b78c925 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -270,11 +270,11 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
> if (user_mode(regs)) {
> ulong syscall = regs->a7;
>
> - syscall = syscall_enter_from_user_mode(regs, syscall);
> -
> regs->epc += 4;
> regs->orig_a0 = regs->a0;
>
> + syscall = syscall_enter_from_user_mode(regs, syscall);
> +
> if (syscall < NR_syscalls)
> syscall_handler(regs, syscall);
> else
>
> base-commit: d34a6b715a23ccd9c9d0bc7a475bea59dc3e28b2
> --
> 2.37.2
>
On Mon, Apr 3, 2023 at 8:54 AM Björn Töpel <[email protected]> wrote:
> From: Björn Töpel <[email protected]>
>
> The RISC-V calling convention passes the first argument, and the
> return value in the a0 register. For this reason, the a0 register
> needs some extra care; When handling syscalls, the a0 register is
> saved into regs->orig_a0, so a0 can be properly restored for,
> e.g. interrupted syscalls.
>
> This functionality was broken with the introduction of the generic
> entry patches. Here, a0 was saved into orig_a0 after calling
> syscall_enter_from_user_mode(), which can change regs->a0 for some
> paths, incorrectly restoring a0.
>
> This is resolved, by saving a0 prior doing the
> syscall_enter_from_user_mode() call.
>
> Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
> Reviewed-by: Heiko Stuebner <[email protected]>
> Tested-by: Heiko Stuebner <[email protected]>
> Signed-off-by: Björn Töpel <[email protected]>
Tested-by: Geert Uytterhoeven <[email protected]>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
On Mon, Apr 3, 2023 at 2:54 PM Björn Töpel <[email protected]> wrote:
>
> From: Björn Töpel <[email protected]>
>
> The RISC-V calling convention passes the first argument, and the
> return value in the a0 register. For this reason, the a0 register
> needs some extra care; When handling syscalls, the a0 register is
> saved into regs->orig_a0, so a0 can be properly restored for,
> e.g. interrupted syscalls.
>
> This functionality was broken with the introduction of the generic
> entry patches. Here, a0 was saved into orig_a0 after calling
> syscall_enter_from_user_mode(), which can change regs->a0 for some
> paths, incorrectly restoring a0.
>
> This is resolved, by saving a0 prior doing the
> syscall_enter_from_user_mode() call.
>
> Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
> Reviewed-by: Heiko Stuebner <[email protected]>
> Tested-by: Heiko Stuebner <[email protected]>
> Signed-off-by: Björn Töpel <[email protected]>
This fix works for me, thanks!
Tested-by: Andy Chiu <[email protected]>
On Mon, 03 Apr 2023 08:52:07 +0200, Björn Töpel wrote:
> The RISC-V calling convention passes the first argument, and the
> return value in the a0 register. For this reason, the a0 register
> needs some extra care; When handling syscalls, the a0 register is
> saved into regs->orig_a0, so a0 can be properly restored for,
> e.g. interrupted syscalls.
>
> This functionality was broken with the introduction of the generic
> entry patches. Here, a0 was saved into orig_a0 after calling
> syscall_enter_from_user_mode(), which can change regs->a0 for some
> paths, incorrectly restoring a0.
>
> [...]
Applied, thanks!
[1/1] riscv: entry: Save a0 prior syscall_enter_from_user_mode()
https://git.kernel.org/palmer/c/9c2598d43510
Best regards,
--
Palmer Dabbelt <[email protected]>
Hello:
This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <[email protected]>:
On Mon, 3 Apr 2023 08:52:07 +0200 you wrote:
> From: Björn Töpel <[email protected]>
>
> The RISC-V calling convention passes the first argument, and the
> return value in the a0 register. For this reason, the a0 register
> needs some extra care; When handling syscalls, the a0 register is
> saved into regs->orig_a0, so a0 can be properly restored for,
> e.g. interrupted syscalls.
>
> [...]
Here is the summary with links:
- riscv: entry: Save a0 prior syscall_enter_from_user_mode()
https://git.kernel.org/riscv/c/9c2598d43510
You are awesome, thank you!
--
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