Commit ff7a1679 authored by Ard Biesheuvel's avatar Ard Biesheuvel

arm64: efi: Execute runtime services from a dedicated stack

With the introduction of PRMT in the ACPI subsystem, the EFI rts
workqueue is no longer the only caller of efi_call_virt_pointer() in the
kernel. This means the EFI runtime services lock is no longer sufficient
to manage concurrent calls into firmware, but also that firmware calls
may occur that are not marshalled via the workqueue mechanism, but
originate directly from the caller context.

For added robustness, and to ensure that the runtime services have 8 KiB
of stack space available as per the EFI spec, introduce a spinlock
protected EFI runtime stack of 8 KiB, where the spinlock also ensures
serialization between the EFI rts workqueue (which itself serializes EFI
runtime calls) and other callers of efi_call_virt_pointer().

While at it, use the stack pivot to avoid reloading the shadow call
stack pointer from the ordinary stack, as doing so could produce a
gadget to defeat it.
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
parent a37dac5c
......@@ -25,6 +25,7 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
({ \
efi_virtmap_load(); \
__efi_fpsimd_begin(); \
spin_lock(&efi_rt_lock); \
})
#undef arch_efi_call_virt
......@@ -33,10 +34,12 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
#define arch_efi_call_virt_teardown() \
({ \
spin_unlock(&efi_rt_lock); \
__efi_fpsimd_end(); \
efi_virtmap_unload(); \
})
extern spinlock_t efi_rt_lock;
efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...);
#define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
......
......@@ -16,6 +16,12 @@ SYM_FUNC_START(__efi_rt_asm_wrapper)
*/
stp x1, x18, [sp, #16]
ldr_l x16, efi_rt_stack_top
mov sp, x16
#ifdef CONFIG_SHADOW_CALL_STACK
str x18, [sp, #-16]!
#endif
/*
* We are lucky enough that no EFI runtime services take more than
* 5 arguments, so all are passed in registers rather than via the
......@@ -29,6 +35,7 @@ SYM_FUNC_START(__efi_rt_asm_wrapper)
mov x4, x6
blr x8
mov sp, x29
ldp x1, x2, [sp, #16]
cmp x2, x18
ldp x29, x30, [sp], #32
......@@ -42,6 +49,10 @@ SYM_FUNC_START(__efi_rt_asm_wrapper)
* called with preemption disabled and a separate shadow stack is used
* for interrupts.
*/
mov x18, x2
#ifdef CONFIG_SHADOW_CALL_STACK
ldr_l x18, efi_rt_stack_top
ldr x18, [x18, #-16]
#endif
b efi_handle_corrupted_x18 // tail call
SYM_FUNC_END(__efi_rt_asm_wrapper)
......@@ -144,3 +144,30 @@ asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f)
pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f);
return s;
}
DEFINE_SPINLOCK(efi_rt_lock);
asmlinkage u64 *efi_rt_stack_top __ro_after_init;
/* EFI requires 8 KiB of stack space for runtime services */
static_assert(THREAD_SIZE >= SZ_8K);
static int __init arm64_efi_rt_init(void)
{
void *p;
if (!efi_enabled(EFI_RUNTIME_SERVICES))
return 0;
p = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, GFP_KERNEL,
NUMA_NO_NODE, &&l);
l: if (!p) {
pr_warn("Failed to allocate EFI runtime stack\n");
clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
return -ENOMEM;
}
efi_rt_stack_top = p + THREAD_SIZE;
return 0;
}
core_initcall(arm64_efi_rt_init);
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