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 v1:
- use smp_store_release directly
- use unsigned int instead of atomic_t
arch/riscv/kernel/entry.S | 4 ++++
arch/riscv/kernel/traps.c | 4 ++++
2 files changed, 8 insertions(+)
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index b9eda3fcbd6d..7b924b16792b 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
+ amoswap.w 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..f1f57c1241b6 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -221,11 +221,15 @@ asmlinkage unsigned long get_overflow_stack(void)
OVERFLOW_STACK_SIZE;
}
+unsigned int 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);
+ smp_store_release(&spin_shadow_stack, 0);
+
console_verbose();
pr_emerg("Insufficient stack space to handle exception!\n");
--
2.37.2
On Thu, Oct 20, 2022 at 10:43 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 v1:
> - use smp_store_release directly
> - use unsigned int instead of atomic_t
>
> arch/riscv/kernel/entry.S | 4 ++++
> arch/riscv/kernel/traps.c | 4 ++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index b9eda3fcbd6d..7b924b16792b 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
> + amoswap.w sp, sp, (sp)
Using ".w" is tricky for 64 BIT, I've hesitated. ';)
Let's move to REG_AMOSWAP, or you must make sure the address of
spin_shadow_stack won't be 4GB aligned.
> + 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..f1f57c1241b6 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -221,11 +221,15 @@ asmlinkage unsigned long get_overflow_stack(void)
> OVERFLOW_STACK_SIZE;
> }
>
> +unsigned int 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);
>
> + 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
On Thu, Oct 20, 2022 at 10:33:29PM +0800, Jisheng Zhang 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 v1:
> - use smp_store_release directly
> - use unsigned int instead of atomic_t
>
> arch/riscv/kernel/entry.S | 4 ++++
> arch/riscv/kernel/traps.c | 4 ++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index b9eda3fcbd6d..7b924b16792b 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
> + amoswap.w 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..f1f57c1241b6 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -221,11 +221,15 @@ asmlinkage unsigned long get_overflow_stack(void)
> OVERFLOW_STACK_SIZE;
> }
>
> +unsigned int 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);
>
> + smp_store_release(&spin_shadow_stack, 0);
> +
Maybe add a comment integrating Guo's remarks,
https://lore.kernel.org/all/CAJF2gTRAEX_jQ_w5H05dyafZzHq+P5j05TJ=C+v+OL__GQam4A@mail.gmail.com/T/#u
https://lore.kernel.org/all/CAJF2gTRdtcpccL5W48O8VEXCMvxNAyyrKJzhwNJkc8js+H2iJg@mail.gmail.com/T/#u
It will come in handy to future reviewers (and it would address the
checkpatch.pl's "memory barrier without comment" warning).
Thanks,
Andrea
> console_verbose();
>
> pr_emerg("Insufficient stack space to handle exception!\n");
> --
> 2.37.2
>
>
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