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Commit 96bc0830 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Greg Kroah-Hartman
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BACKPORT: arm64: efi: Execute runtime services from a dedicated stack 



commit ff7a167961d1b97e0e205f245f806e564d3505e7 upstream.

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.

Bug: 260821414
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Cc: Lee Jones <lee@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarLee Jones <joneslee@google.com>
Change-Id: Ie961576ae93cafc315cb37fb84cca0a6402eda59
(cherry picked from commit 67884a649c141a44d91400df6ca0a5ef55e1771a)
[Lee: Swap-out the non-existent __vmalloc_node() for __vmalloc_node_range()]
parent a9acc03a

arch/arm64/include/asm/efi.h

+3 −0
Original line number Diff line number Diff line
@@ -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);					\

})



#define arch_efi_call_virt(p, f, args...)				\
@@ -36,10 +37,12 @@ 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)

arch/arm64/kernel/efi-rt-wrapper.S

+11 −2
Original line number Diff line number Diff line
@@ -19,6 +19,12 @@ ENTRY(__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
@@ -32,19 +38,22 @@ ENTRY(__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

	b.ne	0f

	ret

0:

#ifdef CONFIG_SHADOW_CALL_STACK

	/*

	 * Restore x18 before returning to instrumented code. This is

	 * safe because the wrapper is 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

ENDPROC(__efi_rt_asm_wrapper)

arch/arm64/kernel/efi.c

+28 −0
Original line number Diff line number Diff line
@@ -148,3 +148,31 @@ 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_range(THREAD_SIZE, THREAD_ALIGN, VMALLOC_START,

				 VMALLOC_END, GFP_KERNEL, PAGE_KERNEL, 0,

				 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);