On Wed, Mar 23, 2022 at 04:32:53PM +0100, andrey.konovalov@xxxxxxxxx wrote: > From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > > When an interrupt happens, the current Shadow Call Stack (SCS) pointer > is switched to a per-interrupt one stored in a per-CPU variable. The old > pointer is then saved on the normal stack and restored when the interrupt > is handled. > > To collect the current stack trace based on SCS when the interrupt is > being handled, we need to know the SCS pointers that belonged to the > task and potentially other interrupts that were interrupted. > > Instead of trying to retrieve the SCS pointers from the stack, change > interrupt handlers (for hard IRQ, Normal and Critical SDEI) to save the > previous SCS pointer in a per-CPU variable. I'm *really* not keen on *always* poking this in the entry code for the uncommon case of unwind. It complicates the entry code and means we're always paying a cost for potentially no benefit. At a high-level, I don't think this is the right approach. For the regular unwinder, I want to rework things such that we can identify exception boundaries and look into the regs (e.g. so that we can recover the PC+LR+FP and avoid duplicating part of this in a frame record), and I'd much prefer that we did the same here. Thanks, Mark. > Note that interrupts stack. A task can be interrupted by a hard IRQ, > which then can interrupted by a normal SDEI, etc. This is handled by > using a separate per-CPU variable for each interrupt type. > > Also reset the saved SCS pointer when exiting the interrupt. This allows > checking whether we should include any interrupt frames when collecting > the stack trace. While we could use in_hardirq(), there seems to be no > easy way to check whether we are in an SDEI handler. Directly checking > the per-CPU variables for being non-zero is more resilient. > > Also expose both the the added saved SCS variables and the existing SCS > base variables in arch/arm64/include/asm/scs.h so that the stack trace > collection impementation can use them. > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > --- > arch/arm64/include/asm/assembler.h | 12 ++++++++++++ > arch/arm64/include/asm/scs.h | 13 ++++++++++++- > arch/arm64/kernel/entry.S | 28 ++++++++++++++++++++++++---- > arch/arm64/kernel/irq.c | 4 +--- > arch/arm64/kernel/sdei.c | 5 ++--- > 5 files changed, 51 insertions(+), 11 deletions(-) > > diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h > index 8c5a61aeaf8e..ca018e981d13 100644 > --- a/arch/arm64/include/asm/assembler.h > +++ b/arch/arm64/include/asm/assembler.h > @@ -270,6 +270,18 @@ alternative_endif > ldr \dst, [\dst, \tmp] > .endm > > + /* > + * @src: Register whose value gets stored in sym > + * @sym: The name of the per-cpu variable > + * @tmp0: Scratch register > + * @tmp1: Another scratch register > + */ > + .macro str_this_cpu src, sym, tmp0, tmp1 > + adr_l \tmp0, \sym > + get_this_cpu_offset \tmp1 > + str \src, [\tmp0, \tmp1] > + .endm > + > /* > * vma_vm_mm - get mm pointer from vma pointer (vma->vm_mm) > */ > diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h > index 8297bccf0784..2bb2b32f787b 100644 > --- a/arch/arm64/include/asm/scs.h > +++ b/arch/arm64/include/asm/scs.h > @@ -24,6 +24,17 @@ > .endm > #endif /* CONFIG_SHADOW_CALL_STACK */ > > -#endif /* __ASSEMBLY __ */ > +#else /* __ASSEMBLY__ */ > + > +#include <linux/percpu.h> > + > +DECLARE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr); > +DECLARE_PER_CPU(unsigned long *, irq_shadow_call_stack_saved_ptr); > +DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr); > +DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_saved_ptr); > +DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr); > +DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_saved_ptr); > + > +#endif /* __ASSEMBLY__ */ > > #endif /* _ASM_SCS_H */ > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index ede028dee81b..1c62fecda172 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -880,7 +880,8 @@ NOKPROBE(ret_from_fork) > */ > SYM_FUNC_START(call_on_irq_stack) > #ifdef CONFIG_SHADOW_CALL_STACK > - stp scs_sp, xzr, [sp, #-16]! > + /* Save the current SCS pointer and load the per-IRQ one. */ > + str_this_cpu scs_sp, irq_shadow_call_stack_saved_ptr, x15, x17 > 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) */ > @@ -902,7 +903,9 @@ 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 > + /* Restore saved SCS pointer and reset the saved value. */ > + ldr_this_cpu scs_sp, irq_shadow_call_stack_saved_ptr, x17 > + str_this_cpu xzr, irq_shadow_call_stack_saved_ptr, x15, x17 > #endif > ret > SYM_FUNC_END(call_on_irq_stack) > @@ -1024,11 +1027,16 @@ SYM_CODE_START(__sdei_asm_handler) > #endif > > #ifdef CONFIG_SHADOW_CALL_STACK > - /* Use a separate shadow call stack for normal and critical events */ > + /* > + * Use a separate shadow call stack for normal and critical events. > + * Save the current SCS pointer and load the per-SDEI one. > + */ > cbnz w4, 3f > + str_this_cpu src=scs_sp, sym=sdei_shadow_call_stack_normal_saved_ptr, tmp0=x5, tmp1=x6 > ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_normal_ptr, tmp=x6 > b 4f > -3: ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_critical_ptr, tmp=x6 > +3: str_this_cpu src=scs_sp, sym=sdei_shadow_call_stack_critical_saved_ptr, tmp0=x5, tmp1=x6 > + ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_critical_ptr, tmp=x6 > 4: > #endif > > @@ -1062,6 +1070,18 @@ SYM_CODE_START(__sdei_asm_handler) > ldp lr, x1, [x4, #SDEI_EVENT_INTREGS + S_LR] > mov sp, x1 > > +#ifdef CONFIG_SHADOW_CALL_STACK > + /* Restore saved SCS pointer and reset the saved value. */ > + ldrb w5, [x4, #SDEI_EVENT_PRIORITY] > + cbnz w5, 5f > + ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_normal_saved_ptr, tmp=x6 > + str_this_cpu src=xzr, sym=sdei_shadow_call_stack_normal_saved_ptr, tmp0=x5, tmp1=x6 > + b 6f > +5: ldr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_critical_saved_ptr, tmp=x6 > + str_this_cpu src=xzr, sym=sdei_shadow_call_stack_critical_saved_ptr, tmp0=x5, tmp1=x6 > +6: > +#endif > + > mov x1, x0 // address to complete_and_resume > /* x0 = (x0 <= SDEI_EV_FAILED) ? > * EVENT_COMPLETE:EVENT_COMPLETE_AND_RESUME > diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c > index bda49430c9ea..4199f900714a 100644 > --- a/arch/arm64/kernel/irq.c > +++ b/arch/arm64/kernel/irq.c > @@ -28,11 +28,9 @@ DEFINE_PER_CPU(struct nmi_ctx, nmi_contexts); > > DEFINE_PER_CPU(unsigned long *, irq_stack_ptr); > > - > -DECLARE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr); > - > #ifdef CONFIG_SHADOW_CALL_STACK > DEFINE_PER_CPU(unsigned long *, irq_shadow_call_stack_ptr); > +DEFINE_PER_CPU(unsigned long *, irq_shadow_call_stack_saved_ptr); > #endif > > static void init_irq_scs(void) > diff --git a/arch/arm64/kernel/sdei.c b/arch/arm64/kernel/sdei.c > index d20620a1c51a..269adcb9e854 100644 > --- a/arch/arm64/kernel/sdei.c > +++ b/arch/arm64/kernel/sdei.c > @@ -39,12 +39,11 @@ DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr); > DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr); > #endif > > -DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr); > -DECLARE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr); > - > #ifdef CONFIG_SHADOW_CALL_STACK > DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_ptr); > +DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_normal_saved_ptr); > DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_ptr); > +DEFINE_PER_CPU(unsigned long *, sdei_shadow_call_stack_critical_saved_ptr); > #endif > > static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu) > -- > 2.25.1 >
