2022-09-20 15:42:09

by Chen Zhongjin

Subject: [PATCH -next 4/7] riscv: syscall: Don't clobber s0 when syscall

syscall uses s0 to load address of sys_call_table.

Since now we uses s0 to save pt_regs for unwinding, clobber
s0 can make unwinder treat s0 as pt_regs address. Use s1 for
this job.

Signed-off-by: Chen Zhongjin <[email protected]>
---
arch/riscv/kernel/entry.S | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index ecb15c7430b4..a3b14a649782 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -205,33 +205,33 @@ handle_syscall:
check_syscall_nr:
/* Check to make sure we don't jump to a bogus syscall number. */
li t0, __NR_syscalls
- la s0, sys_ni_syscall
+ la s1, sys_ni_syscall
/*
* Syscall number held in a7.
* If syscall number is above allowed value, redirect to ni_syscall.
*/
bgeu a7, t0, 3f
#ifdef CONFIG_COMPAT
- REG_L s0, PT_STATUS(sp)
- srli s0, s0, SR_UXL_SHIFT
- andi s0, s0, (SR_UXL >> SR_UXL_SHIFT)
+ REG_L s1, PT_STATUS(sp)
+ srli s1, s1, SR_UXL_SHIFT
+ andi s1, s1, (SR_UXL >> SR_UXL_SHIFT)
li t0, (SR_UXL_32 >> SR_UXL_SHIFT)
- sub t0, s0, t0
+ sub t0, s1, t0
bnez t0, 1f

/* Call compat_syscall */
- la s0, compat_sys_call_table
+ la s1, compat_sys_call_table
j 2f
1:
#endif
/* Call syscall */
- la s0, sys_call_table
+ la s1, sys_call_table
2:
slli t0, a7, RISCV_LGPTR
- add s0, s0, t0
- REG_L s0, 0(s0)
+ add s1, s1, t0
+ REG_L s1, 0(s1)
3:
- jalr s0
+ jalr s1

ret_from_syscall:
/* Set user a0 to kernel a0 */
--
2.17.1

2022-09-21 01:44:17

by Guo Ren

Subject: Re: [PATCH -next 4/7] riscv: syscall: Don't clobber s0 when syscall

On Tue, Sep 20, 2022 at 11:15 PM Chen Zhongjin <[email protected]> wrote:
>
> syscall uses s0 to load address of sys_call_table.
>
> Since now we uses s0 to save pt_regs for unwinding, clobber
> s0 can make unwinder treat s0 as pt_regs address. Use s1 for
> this job.
This patch does not make sense. Why couldn't we use s1 for pt_regs?

No need to modify the entry.S here.

>
> Signed-off-by: Chen Zhongjin <[email protected]>
> ---
> arch/riscv/kernel/entry.S | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index ecb15c7430b4..a3b14a649782 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -205,33 +205,33 @@ handle_syscall:
> check_syscall_nr:
> /* Check to make sure we don't jump to a bogus syscall number. */
> li t0, __NR_syscalls
> - la s0, sys_ni_syscall
> + la s1, sys_ni_syscall
> /*
> * Syscall number held in a7.
> * If syscall number is above allowed value, redirect to ni_syscall.
> */
> bgeu a7, t0, 3f
> #ifdef CONFIG_COMPAT
> - REG_L s0, PT_STATUS(sp)
> - srli s0, s0, SR_UXL_SHIFT
> - andi s0, s0, (SR_UXL >> SR_UXL_SHIFT)
> + REG_L s1, PT_STATUS(sp)
> + srli s1, s1, SR_UXL_SHIFT
> + andi s1, s1, (SR_UXL >> SR_UXL_SHIFT)
> li t0, (SR_UXL_32 >> SR_UXL_SHIFT)
> - sub t0, s0, t0
> + sub t0, s1, t0
> bnez t0, 1f
>
> /* Call compat_syscall */
> - la s0, compat_sys_call_table
> + la s1, compat_sys_call_table
> j 2f
> 1:
> #endif
> /* Call syscall */
> - la s0, sys_call_table
> + la s1, sys_call_table
> 2:
> slli t0, a7, RISCV_LGPTR
> - add s0, s0, t0
> - REG_L s0, 0(s0)
> + add s1, s1, t0
> + REG_L s1, 0(s1)
> 3:
> - jalr s0
> + jalr s1
>
> ret_from_syscall:
> /* Set user a0 to kernel a0 */
> --
> 2.17.1
>


--
Best Regards
Guo Ren

2022-09-21 02:32:04

by Guo Ren

Subject: Re: [PATCH -next 4/7] riscv: syscall: Don't clobber s0 when syscall

On Wed, Sep 21, 2022 at 9:30 AM Guo Ren <[email protected]> wrote:
>
> On Tue, Sep 20, 2022 at 11:15 PM Chen Zhongjin <[email protected]> wrote:
> >
> > syscall uses s0 to load address of sys_call_table.
> >
> > Since now we uses s0 to save pt_regs for unwinding, clobber
> > s0 can make unwinder treat s0 as pt_regs address. Use s1 for
> > this job.
> This patch does not make sense. Why couldn't we use s1 for pt_regs?
Seems s0->fp can't be replaced. I take back the question.

>
> No need to modify the entry.S here.
>
> >
> > Signed-off-by: Chen Zhongjin <[email protected]>
> > ---
> > arch/riscv/kernel/entry.S | 20 ++++++++++----------
> > 1 file changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index ecb15c7430b4..a3b14a649782 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -205,33 +205,33 @@ handle_syscall:
> > check_syscall_nr:
> > /* Check to make sure we don't jump to a bogus syscall number. */
> > li t0, __NR_syscalls
> > - la s0, sys_ni_syscall
> > + la s1, sys_ni_syscall
> > /*
> > * Syscall number held in a7.
> > * If syscall number is above allowed value, redirect to ni_syscall.
> > */
> > bgeu a7, t0, 3f
> > #ifdef CONFIG_COMPAT
> > - REG_L s0, PT_STATUS(sp)
> > - srli s0, s0, SR_UXL_SHIFT
> > - andi s0, s0, (SR_UXL >> SR_UXL_SHIFT)
> > + REG_L s1, PT_STATUS(sp)
> > + srli s1, s1, SR_UXL_SHIFT
> > + andi s1, s1, (SR_UXL >> SR_UXL_SHIFT)
> > li t0, (SR_UXL_32 >> SR_UXL_SHIFT)
> > - sub t0, s0, t0
> > + sub t0, s1, t0
> > bnez t0, 1f
> >
> > /* Call compat_syscall */
> > - la s0, compat_sys_call_table
> > + la s1, compat_sys_call_table
> > j 2f
> > 1:
> > #endif
> > /* Call syscall */
> > - la s0, sys_call_table
> > + la s1, sys_call_table
> > 2:
> > slli t0, a7, RISCV_LGPTR
> > - add s0, s0, t0
> > - REG_L s0, 0(s0)
> > + add s1, s1, t0
> > + REG_L s1, 0(s1)
> > 3:
> > - jalr s0
> > + jalr s1
> >
> > ret_from_syscall:
> > /* Set user a0 to kernel a0 */
> > --
> > 2.17.1
> >
>
>
> --
> Best Regards
> Guo Ren



--
Best Regards
Guo Ren