2022-10-30 13:09:40

by Jisheng Zhang

Subject: [PATCH v3] riscv: fix race when vmap stack overflow

Currently, when detecting vmap stack overflow, riscv firstly switches
to the so called shadow stack, then use this shadow stack to call the
get_overflow_stack() to get the overflow stack. However, there's
a race here if two or more harts use the same shadow stack at the same
time.

To solve this race, we introduce spin_shadow_stack atomic var, which
will be swap between its own address and 0 in atomic way, when the
var is set, it means the shadow_stack is being used; when the var
is cleared, it means the shadow_stack isn't being used.

Fixes: 31da94c25aea ("riscv: add VMAP_STACK overflow detection")
Signed-off-by: Jisheng Zhang <[email protected]>
Suggested-by: Guo Ren <[email protected]>
---
Since v2:
- use REG_AMOSWAP
- add comment to the purpose of smp_store_release()

Since v1:
- use smp_store_release directly
- use unsigned int instead of atomic_t


arch/riscv/include/asm/asm.h | 1 +
arch/riscv/kernel/entry.S | 4 ++++
arch/riscv/kernel/traps.c | 9 +++++++++
3 files changed, 14 insertions(+)

diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index 1b471ff73178..acf563072b8b 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -23,6 +23,7 @@
#define REG_L __REG_SEL(ld, lw)
#define REG_S __REG_SEL(sd, sw)
#define REG_SC __REG_SEL(sc.d, sc.w)
+#define REG_AMOSWAP __REG_SEL(amoswap.d, amoswap.w)
#define REG_ASM __REG_SEL(.dword, .word)
#define SZREG __REG_SEL(8, 4)
#define LGREG __REG_SEL(3, 2)
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index b9eda3fcbd6d..ea6b78dac739 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -404,6 +404,10 @@ handle_syscall_trace_exit:

#ifdef CONFIG_VMAP_STACK
handle_kernel_stack_overflow:
+1: la sp, spin_shadow_stack
+ REG_AMOSWAP sp, sp, (sp)
+ bnez sp, 1b
+
la sp, shadow_stack
addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index f3e96d60a2ff..dea47f329708 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -221,11 +221,20 @@ asmlinkage unsigned long get_overflow_stack(void)
OVERFLOW_STACK_SIZE;
}

+unsigned long spin_shadow_stack;
+
asmlinkage void handle_bad_stack(struct pt_regs *regs)
{
unsigned long tsk_stk = (unsigned long)current->stack;
unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);

+ /*
+ * to ensure spin flag is set after the sp is used in entry.S:
+ * //load per-cpu overflow stack.
+ * REG_L sp, -8(sp)
+ */
+ smp_store_release(&spin_shadow_stack, 0);
+
console_verbose();

pr_emerg("Insufficient stack space to handle exception!\n");
--
2.37.2

2022-10-30 13:39:14

by Guo Ren

Subject: Re: [PATCH v3] riscv: fix race when vmap stack overflow

Reviewed-by: Guo Ren <[email protected]>

On Sun, Oct 30, 2022 at 8:54 PM Jisheng Zhang <[email protected]> wrote:
>
> Currently, when detecting vmap stack overflow, riscv firstly switches
> to the so called shadow stack, then use this shadow stack to call the
> get_overflow_stack() to get the overflow stack. However, there's
> a race here if two or more harts use the same shadow stack at the same
> time.
>
> To solve this race, we introduce spin_shadow_stack atomic var, which
> will be swap between its own address and 0 in atomic way, when the
> var is set, it means the shadow_stack is being used; when the var
> is cleared, it means the shadow_stack isn't being used.
>
> Fixes: 31da94c25aea ("riscv: add VMAP_STACK overflow detection")
> Signed-off-by: Jisheng Zhang <[email protected]>
> Suggested-by: Guo Ren <[email protected]>
> ---
> Since v2:
> - use REG_AMOSWAP
> - add comment to the purpose of smp_store_release()
>
> Since v1:
> - use smp_store_release directly
> - use unsigned int instead of atomic_t
>
>
> arch/riscv/include/asm/asm.h | 1 +
> arch/riscv/kernel/entry.S | 4 ++++
> arch/riscv/kernel/traps.c | 9 +++++++++
> 3 files changed, 14 insertions(+)
>
> diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
> index 1b471ff73178..acf563072b8b 100644
> --- a/arch/riscv/include/asm/asm.h
> +++ b/arch/riscv/include/asm/asm.h
> @@ -23,6 +23,7 @@
> #define REG_L __REG_SEL(ld, lw)
> #define REG_S __REG_SEL(sd, sw)
> #define REG_SC __REG_SEL(sc.d, sc.w)
> +#define REG_AMOSWAP __REG_SEL(amoswap.d, amoswap.w)
> #define REG_ASM __REG_SEL(.dword, .word)
> #define SZREG __REG_SEL(8, 4)
> #define LGREG __REG_SEL(3, 2)
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index b9eda3fcbd6d..ea6b78dac739 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -404,6 +404,10 @@ handle_syscall_trace_exit:
>
> #ifdef CONFIG_VMAP_STACK
> handle_kernel_stack_overflow:
> +1: la sp, spin_shadow_stack
> + REG_AMOSWAP sp, sp, (sp)
> + bnez sp, 1b
> +
> la sp, shadow_stack
> addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE
>
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index f3e96d60a2ff..dea47f329708 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -221,11 +221,20 @@ asmlinkage unsigned long get_overflow_stack(void)
> OVERFLOW_STACK_SIZE;
> }
>
> +unsigned long spin_shadow_stack;
> +
> asmlinkage void handle_bad_stack(struct pt_regs *regs)
> {
> unsigned long tsk_stk = (unsigned long)current->stack;
> unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
>
> + /*
> + * to ensure spin flag is set after the sp is used in entry.S:
> + * //load per-cpu overflow stack.
> + * REG_L sp, -8(sp)
> + */
> + smp_store_release(&spin_shadow_stack, 0);
> +
> console_verbose();
>
> pr_emerg("Insufficient stack space to handle exception!\n");
> --
> 2.37.2
>


--
Best Regards
Guo Ren

2022-11-23 15:50:25

by Jisheng Zhang

Subject: Re: [PATCH v3] riscv: fix race when vmap stack overflow

On Sun, Oct 30, 2022 at 09:23:51PM +0800, Guo Ren wrote:
> Reviewed-by: Guo Ren <[email protected]>
>

Gentle ping? This patch is still missing in mainline.

> On Sun, Oct 30, 2022 at 8:54 PM Jisheng Zhang <[email protected]> wrote:
> >
> > Currently, when detecting vmap stack overflow, riscv firstly switches
> > to the so called shadow stack, then use this shadow stack to call the
> > get_overflow_stack() to get the overflow stack. However, there's
> > a race here if two or more harts use the same shadow stack at the same
> > time.
> >
> > To solve this race, we introduce spin_shadow_stack atomic var, which
> > will be swap between its own address and 0 in atomic way, when the
> > var is set, it means the shadow_stack is being used; when the var
> > is cleared, it means the shadow_stack isn't being used.
> >
> > Fixes: 31da94c25aea ("riscv: add VMAP_STACK overflow detection")
> > Signed-off-by: Jisheng Zhang <[email protected]>
> > Suggested-by: Guo Ren <[email protected]>
> > ---
> > Since v2:
> > - use REG_AMOSWAP
> > - add comment to the purpose of smp_store_release()
> >
> > Since v1:
> > - use smp_store_release directly
> > - use unsigned int instead of atomic_t
> >
> >
> > arch/riscv/include/asm/asm.h | 1 +
> > arch/riscv/kernel/entry.S | 4 ++++
> > arch/riscv/kernel/traps.c | 9 +++++++++
> > 3 files changed, 14 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
> > index 1b471ff73178..acf563072b8b 100644
> > --- a/arch/riscv/include/asm/asm.h
> > +++ b/arch/riscv/include/asm/asm.h
> > @@ -23,6 +23,7 @@
> > #define REG_L __REG_SEL(ld, lw)
> > #define REG_S __REG_SEL(sd, sw)
> > #define REG_SC __REG_SEL(sc.d, sc.w)
> > +#define REG_AMOSWAP __REG_SEL(amoswap.d, amoswap.w)
> > #define REG_ASM __REG_SEL(.dword, .word)
> > #define SZREG __REG_SEL(8, 4)
> > #define LGREG __REG_SEL(3, 2)
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index b9eda3fcbd6d..ea6b78dac739 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -404,6 +404,10 @@ handle_syscall_trace_exit:
> >
> > #ifdef CONFIG_VMAP_STACK
> > handle_kernel_stack_overflow:
> > +1: la sp, spin_shadow_stack
> > + REG_AMOSWAP sp, sp, (sp)
> > + bnez sp, 1b
> > +
> > la sp, shadow_stack
> > addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE
> >
> > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > index f3e96d60a2ff..dea47f329708 100644
> > --- a/arch/riscv/kernel/traps.c
> > +++ b/arch/riscv/kernel/traps.c
> > @@ -221,11 +221,20 @@ asmlinkage unsigned long get_overflow_stack(void)
> > OVERFLOW_STACK_SIZE;
> > }
> >
> > +unsigned long spin_shadow_stack;
> > +
> > asmlinkage void handle_bad_stack(struct pt_regs *regs)
> > {
> > unsigned long tsk_stk = (unsigned long)current->stack;
> > unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
> >
> > + /*
> > + * to ensure spin flag is set after the sp is used in entry.S:
> > + * //load per-cpu overflow stack.
> > + * REG_L sp, -8(sp)
> > + */
> > + smp_store_release(&spin_shadow_stack, 0);
> > +
> > console_verbose();
> >
> > pr_emerg("Insufficient stack space to handle exception!\n");
> > --
> > 2.37.2
> >
>
>
> --
> Best Regards
> Guo Ren

2022-11-30 03:00:17

by Palmer Dabbelt

Subject: Re: [PATCH v3] riscv: fix race when vmap stack overflow

On Wed, 23 Nov 2022 07:23:51 PST (-0800), [email protected] wrote:
> On Sun, Oct 30, 2022 at 09:23:51PM +0800, Guo Ren wrote:
>> Reviewed-by: Guo Ren <[email protected]>
>>
>
> Gentle ping? This patch is still missing in mainline.

Sorry, this one took a few looks to figure out. I just sent out a v4,
it's pretty much the same thing but by the time I'd figured out what
this was doing it seemed easier to just write up the comments directly.

https://lore.kernel.org/r/[email protected]/

I'll try and watch the threads, LMK if I screwed anything up. I've
already got this queued up in staging so it's being tested, should be
fast to take it onto fixes.

Thanks!

>
>> On Sun, Oct 30, 2022 at 8:54 PM Jisheng Zhang <[email protected]> wrote:
>> >
>> > Currently, when detecting vmap stack overflow, riscv firstly switches
>> > to the so called shadow stack, then use this shadow stack to call the
>> > get_overflow_stack() to get the overflow stack. However, there's
>> > a race here if two or more harts use the same shadow stack at the same
>> > time.
>> >
>> > To solve this race, we introduce spin_shadow_stack atomic var, which
>> > will be swap between its own address and 0 in atomic way, when the
>> > var is set, it means the shadow_stack is being used; when the var
>> > is cleared, it means the shadow_stack isn't being used.
>> >
>> > Fixes: 31da94c25aea ("riscv: add VMAP_STACK overflow detection")
>> > Signed-off-by: Jisheng Zhang <[email protected]>
>> > Suggested-by: Guo Ren <[email protected]>
>> > ---
>> > Since v2:
>> > - use REG_AMOSWAP
>> > - add comment to the purpose of smp_store_release()
>> >
>> > Since v1:
>> > - use smp_store_release directly
>> > - use unsigned int instead of atomic_t
>> >
>> >
>> > arch/riscv/include/asm/asm.h | 1 +
>> > arch/riscv/kernel/entry.S | 4 ++++
>> > arch/riscv/kernel/traps.c | 9 +++++++++
>> > 3 files changed, 14 insertions(+)
>> >
>> > diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
>> > index 1b471ff73178..acf563072b8b 100644
>> > --- a/arch/riscv/include/asm/asm.h
>> > +++ b/arch/riscv/include/asm/asm.h
>> > @@ -23,6 +23,7 @@
>> > #define REG_L __REG_SEL(ld, lw)
>> > #define REG_S __REG_SEL(sd, sw)
>> > #define REG_SC __REG_SEL(sc.d, sc.w)
>> > +#define REG_AMOSWAP __REG_SEL(amoswap.d, amoswap.w)
>> > #define REG_ASM __REG_SEL(.dword, .word)
>> > #define SZREG __REG_SEL(8, 4)
>> > #define LGREG __REG_SEL(3, 2)
>> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
>> > index b9eda3fcbd6d..ea6b78dac739 100644
>> > --- a/arch/riscv/kernel/entry.S
>> > +++ b/arch/riscv/kernel/entry.S
>> > @@ -404,6 +404,10 @@ handle_syscall_trace_exit:
>> >
>> > #ifdef CONFIG_VMAP_STACK
>> > handle_kernel_stack_overflow:
>> > +1: la sp, spin_shadow_stack
>> > + REG_AMOSWAP sp, sp, (sp)
>> > + bnez sp, 1b
>> > +
>> > la sp, shadow_stack
>> > addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE
>> >
>> > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
>> > index f3e96d60a2ff..dea47f329708 100644
>> > --- a/arch/riscv/kernel/traps.c
>> > +++ b/arch/riscv/kernel/traps.c
>> > @@ -221,11 +221,20 @@ asmlinkage unsigned long get_overflow_stack(void)
>> > OVERFLOW_STACK_SIZE;
>> > }
>> >
>> > +unsigned long spin_shadow_stack;
>> > +
>> > asmlinkage void handle_bad_stack(struct pt_regs *regs)
>> > {
>> > unsigned long tsk_stk = (unsigned long)current->stack;
>> > unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
>> >
>> > + /*
>> > + * to ensure spin flag is set after the sp is used in entry.S:
>> > + * //load per-cpu overflow stack.
>> > + * REG_L sp, -8(sp)
>> > + */
>> > + smp_store_release(&spin_shadow_stack, 0);
>> > +
>> > console_verbose();
>> >
>> > pr_emerg("Insufficient stack space to handle exception!\n");
>> > --
>> > 2.37.2
>> >
>>
>>
>> --
>> Best Regards
>> Guo Ren