| Message ID | 20230109174800.3286265-3-ardb@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: harden shadow call stack pointer handling | expand |
On Mon, Jan 09, 2023 at 06:48:00PM +0100, Ard Biesheuvel wrote: > Instead of reloading the shadow call stack pointer from the ordinary > stack, which may be vulnerable to the kind of gadget based attacks > shadow call stacks were designed to prevent, let's store a task's shadow > call stack pointer in the task struct when switching to the shadow IRQ > stack. > > Given that currently, the task_struct::scs_sp field is only used to > preserve the shadow call stack pointer while a task is scheduled out or > running in user space, reusing this field to preserve and restore it > while running off the IRQ stack must be safe, as those occurrences are > guaranteed to never overlap. (The stack switching logic only switches > stacks when running from the task stack, and so the value being saved > here always corresponds to the task mode shadow stack) > > While at it, fold a mov/add/mov sequence into a single add. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Mark. > --- > arch/arm64/kernel/entry.S | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 546f7773238ea45d..80d763e165fc5856 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -876,19 +876,19 @@ NOKPROBE(ret_from_fork) > */ > SYM_FUNC_START(call_on_irq_stack) > #ifdef CONFIG_SHADOW_CALL_STACK > - stp scs_sp, xzr, [sp, #-16]! > + get_current_task x16 > + scs_save x16 > ldr_this_cpu scs_sp, irq_shadow_call_stack_ptr, x17 > #endif > + > /* Create a frame record to save our LR and SP (implicit in FP) */ > stp x29, x30, [sp, #-16]! > mov x29, sp > > ldr_this_cpu x16, irq_stack_ptr, x17 > - mov x15, #IRQ_STACK_SIZE > - add x16, x16, x15 > > /* Move to the new stack and call the function there */ > - mov sp, x16 > + add sp, x16, #IRQ_STACK_SIZE > blr x1 > > /* > @@ -897,9 +897,7 @@ SYM_FUNC_START(call_on_irq_stack) > */ > mov sp, x29 > ldp x29, x30, [sp], #16 > -#ifdef CONFIG_SHADOW_CALL_STACK > - ldp scs_sp, xzr, [sp], #16 > -#endif > + scs_load_current > ret > SYM_FUNC_END(call_on_irq_stack) > NOKPROBE(call_on_irq_stack) > -- > 2.39.0 >
On Mon, Jan 09, 2023 at 06:48:00PM +0100, Ard Biesheuvel wrote: > Instead of reloading the shadow call stack pointer from the ordinary > stack, which may be vulnerable to the kind of gadget based attacks > shadow call stacks were designed to prevent, let's store a task's shadow > call stack pointer in the task struct when switching to the shadow IRQ > stack. > > Given that currently, the task_struct::scs_sp field is only used to > preserve the shadow call stack pointer while a task is scheduled out or > running in user space, reusing this field to preserve and restore it > while running off the IRQ stack must be safe, as those occurrences are > guaranteed to never overlap. (The stack switching logic only switches > stacks when running from the task stack, and so the value being saved > here always corresponds to the task mode shadow stack) > > While at it, fold a mov/add/mov sequence into a single add. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 546f7773238ea45d..80d763e165fc5856 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -876,19 +876,19 @@ NOKPROBE(ret_from_fork) */ SYM_FUNC_START(call_on_irq_stack) #ifdef CONFIG_SHADOW_CALL_STACK - stp scs_sp, xzr, [sp, #-16]! + get_current_task x16 + scs_save x16 ldr_this_cpu scs_sp, irq_shadow_call_stack_ptr, x17 #endif + /* Create a frame record to save our LR and SP (implicit in FP) */ stp x29, x30, [sp, #-16]! mov x29, sp ldr_this_cpu x16, irq_stack_ptr, x17 - mov x15, #IRQ_STACK_SIZE - add x16, x16, x15 /* Move to the new stack and call the function there */ - mov sp, x16 + add sp, x16, #IRQ_STACK_SIZE blr x1 /* @@ -897,9 +897,7 @@ SYM_FUNC_START(call_on_irq_stack) */ mov sp, x29 ldp x29, x30, [sp], #16 -#ifdef CONFIG_SHADOW_CALL_STACK - ldp scs_sp, xzr, [sp], #16 -#endif + scs_load_current ret SYM_FUNC_END(call_on_irq_stack) NOKPROBE(call_on_irq_stack)
Instead of reloading the shadow call stack pointer from the ordinary stack, which may be vulnerable to the kind of gadget based attacks shadow call stacks were designed to prevent, let's store a task's shadow call stack pointer in the task struct when switching to the shadow IRQ stack. Given that currently, the task_struct::scs_sp field is only used to preserve the shadow call stack pointer while a task is scheduled out or running in user space, reusing this field to preserve and restore it while running off the IRQ stack must be safe, as those occurrences are guaranteed to never overlap. (The stack switching logic only switches stacks when running from the task stack, and so the value being saved here always corresponds to the task mode shadow stack) While at it, fold a mov/add/mov sequence into a single add. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/arm64/kernel/entry.S | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)