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arm64: efi: Avoid workqueue to check whether EFI runtime is live

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Comparing current_work() against efi_rts_work.work is sufficient to
decide whether current is currently running EFI runtime services code at
any level in its call stack.

However, there are other potential users of the EFI runtime stack, such
as the ACPI subsystem, which may invoke efi_call_virt_pointer()
directly, and so any sync exceptions occurring in firmware during those
calls are currently misidentified.

So instead, let's check whether the stashed value of the thread stack
pointer points into current's thread stack. This can only be the case if
current was interrupted while running EFI runtime code. Note that this
implies that we should clear the stashed value after switching back, to
avoid false positives.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Ard Biesheuvel 2022-10-28 16:39:14 +02:00
parent d3f450533b
commit 8a9a1a1873
3 changed files with 17 additions and 1 deletions
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9
arch/arm64/include/asm/efi.h
View file

@ -48,8 +48,17 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
})
extern spinlock_t efi_rt_lock;
extern u64 *efi_rt_stack_top;
efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...);
/*
* efi_rt_stack_top[-1] contains the value the stack pointer had before
* switching to the EFI runtime stack.
*/
#define current_in_efi() \
(!preemptible() && efi_rt_stack_top != NULL && \
on_task_stack(current, READ_ONCE(efi_rt_stack_top[-1]), 1))
#define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
/*

6
arch/arm64/kernel/efi-rt-wrapper.S
View file

@ -46,7 +46,10 @@ SYM_FUNC_START(__efi_rt_asm_wrapper)
mov x4, x6
blr x8
mov x16, sp
mov sp, x29
str xzr, [x16, #8] // clear recorded task SP value
ldp x1, x2, [sp, #16]
cmp x2, x18
ldp x29, x30, [sp], #112
@ -71,6 +74,9 @@ SYM_FUNC_END(__efi_rt_asm_wrapper)
SYM_CODE_START(__efi_rt_asm_recover)
mov sp, x30
ldr_l x16, efi_rt_stack_top // clear recorded task SP value
str xzr, [x16, #-8]
ldp x19, x20, [sp, #32]
ldp x21, x22, [sp, #48]
ldp x23, x24, [sp, #64]

3
arch/arm64/kernel/efi.c
View file

@ -11,6 +11,7 @@
#include <linux/init.h>
#include <asm/efi.h>
#include <asm/stacktrace.h>
static bool region_is_misaligned(const efi_memory_desc_t *md)
{
@ -154,7 +155,7 @@ asmlinkage efi_status_t __efi_rt_asm_recover(void);
bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg)
{
/* Check whether the exception occurred while running the firmware */
if (current_work() != &efi_rts_work.work || regs->pc >= TASK_SIZE_64)
if (!current_in_efi() || regs->pc >= TASK_SIZE_64)
return false;
pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg);