| Message ID | 20221020143329.3276-1-jszhang@kernel.org (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [v2] riscv: fix race when vmap stack overflow | expand |
On Thu, Oct 20, 2022 at 10:43 PM Jisheng Zhang <jszhang@kernel.org> 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 <jszhang@kernel.org> > Suggested-by: Guo Ren <guoren@kernel.org> > --- > 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 >
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 <jszhang@kernel.org> > Suggested-by: Guo Ren <guoren@kernel.org> > --- > 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 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv
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");
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 <jszhang@kernel.org> Suggested-by: Guo Ren <guoren@kernel.org> --- 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(+)