On Fri, Dec 09, 2022 at 02:34:14PM +0100, Ard Biesheuvel wrote:
> The EFI runtime services run from a dedicated stack now, and so the
> stack unwinder needs to be informed about this.
>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
>
> I realised while looking into this that comparing current_work() against
> efi_rts_work.work is not sufficient to decide whether current is running
> EFI code, given that the ACPI subsystem will call efi_call_virt_pointer()
> directly.
>
> So instead, we can check whether the stashed thread stack pointer value
> matches current's thread stack if the EFI runtime stack is currently in
> use:
>
> #define current_in_efi() \
> (!preemptible() && spin_is_locked(&efi_rt_lock) && \
> on_task_stack(current, efi_rt_stack_top[-1], 1))
Unless you're overwriting task_struct::stack (which seems scary to me), that
doesn't look right; on_task_stack() checks whether a given base + size is on
the stack allocated for the task (i.e. task_struct::stack + THREAD_SIZE), not
the stack the task is currently using.
I would expect this to be something like:
#define current_in_efi() \
(!preemptible() && spin_is_locked(&efi_rt_lock) && \
stackinfo_on_stack(stackinfo_get_efi(), current_stack_pointer, 1))
... or an inline function given this is sufficiently painful as a macro.
... unless I've confused myself?
FWIW, the patch belows looks good to me!
Mark.
> but this will be folded into the preceding patch, which I am not
> reproducing here.
>
> arch/arm64/include/asm/stacktrace.h | 15 +++++++++++++++
> arch/arm64/kernel/stacktrace.c | 12 ++++++++++++
> 2 files changed, 27 insertions(+)
>
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index 5a0edb064ea478bb..327cdcfcb1db0ad5 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -104,4 +104,19 @@ static inline struct stack_info stackinfo_get_sdei_critical(void)
> #define stackinfo_get_sdei_critical() stackinfo_get_unknown()
> #endif
>
> +#ifdef CONFIG_EFI
> +extern u64 *efi_rt_stack_top;
> +
> +static inline struct stack_info stackinfo_get_efi(void)
> +{
> + unsigned long high = (u64)efi_rt_stack_top;
> + unsigned long low = high - THREAD_SIZE;
> +
> + return (struct stack_info) {
> + .low = low,
> + .high = high,
> + };
> +}
> +#endif
> +
> #endif /* __ASM_STACKTRACE_H */
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 634279b3b03d1b07..ee9fd2018cd75ed2 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -5,6 +5,7 @@
> * Copyright (C) 2012 ARM Ltd.
> */
> #include <linux/kernel.h>
> +#include <linux/efi.h>
> #include <linux/export.h>
> #include <linux/ftrace.h>
> #include <linux/sched.h>
> @@ -12,6 +13,7 @@
> #include <linux/sched/task_stack.h>
> #include <linux/stacktrace.h>
>
> +#include <asm/efi.h>
> #include <asm/irq.h>
> #include <asm/stack_pointer.h>
> #include <asm/stacktrace.h>
> @@ -186,6 +188,13 @@ void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
> : stackinfo_get_unknown(); \
> })
>
> +#define STACKINFO_EFI \
> + ({ \
> + ((task == current) && current_in_efi()) \
> + ? stackinfo_get_efi() \
> + : stackinfo_get_unknown(); \
> + })
> +
> noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
> void *cookie, struct task_struct *task,
> struct pt_regs *regs)
> @@ -199,6 +208,9 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
> #if defined(CONFIG_VMAP_STACK) && defined(CONFIG_ARM_SDE_INTERFACE)
> STACKINFO_SDEI(normal),
> STACKINFO_SDEI(critical),
> +#endif
> +#ifdef CONFIG_EFI
> + STACKINFO_EFI,
> #endif
> };
> struct unwind_state state = {
> --
> 2.35.1
>
