efi/libstub/arm: Make efi_entry() an ordinary PE/COFF entrypoint

Expose efi_entry() as the PE/COFF entrypoint directly, instead of
jumping into a wrapper that fiddles with stack buffers and other
stuff that the compiler is much better at. The only reason this
code exists is to obtain a pointer to the base of the image, but
we can get the same value from the loaded_image protocol, which
we already need for other reasons anyway.

Update the return type as well, to make it consistent with what
is required for a PE/COFF executable entrypoint.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 9 insertions, 33 deletions

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 8487221bedb0..36ffbeecd30b 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -1437,33 +1437,15 @@ __enter_kernel:
 reloc_code_end:
 
 #ifdef CONFIG_EFI_STUB
-		.align	2
-_start:		.long	start - .
-
-ENTRY(efi_stub_entry)
-		@ allocate space on stack for passing current zImage address
-		@ and for the EFI stub to return of new entry point of
-		@ zImage, as EFI stub may copy the kernel. Pointer address
-		@ is passed in r2. r0 and r1 are passed through from the
-		@ EFI firmware to efi_entry
-		adr	ip, _start
-		ldr	r3, [ip]
-		add	r3, r3, ip
-		stmfd	sp!, {r3, lr}
-		mov	r2, sp			@ pass zImage address in r2
-		bl	efi_entry
-
-		@ Check for error return from EFI stub. r0 has FDT address
-		@ or error code.
-		cmn	r0, #1
-		beq	efi_load_fail
-
-		@ Preserve return value of efi_entry() in r4
-		mov	r4, r0
-		add	r1, r4, #SZ_2M			@ DT end
+ENTRY(efi_enter_kernel)
+		mov	r7, r0				@ preserve image base
+		mov	r4, r1				@ preserve DT pointer
+
+		mov	r0, r4				@ DT start
+		add	r1, r4, r2			@ DT end
 		bl	cache_clean_flush
 
-		ldr	r0, [sp]			@ relocated zImage
+		mov	r0, r7				@ relocated zImage
 		ldr	r1, =_edata			@ size of zImage
 		add	r1, r1, r0			@ end of zImage
 		bl	cache_clean_flush
@@ -1473,9 +1455,8 @@ ENTRY(efi_stub_entry)
 		@ inside the PE/COFF loader allocated region is unsafe. Let's
 		@ assume our own zImage relocation code did a better job, and
 		@ jump into its version of this routine before proceeding.
-		ldr	r0, [sp]			@ relocated zImage
 		ldr	r1, .Ljmp
-		sub	r1, r0, r1
+		sub	r1, r7, r1
 		mov	pc, r1				@ no mode switch
 0:
 		bl	cache_off
@@ -1487,12 +1468,7 @@ ENTRY(efi_stub_entry)
 		mov	r1, #0xFFFFFFFF
 		mov	r2, r4
 		b	__efi_start
-
-efi_load_fail:
-		@ Return EFI_LOAD_ERROR to EFI firmware on error.
-		ldr	r0, =0x80000001
-		ldmfd	sp!, {ip, pc}
-ENDPROC(efi_stub_entry)
+ENDPROC(efi_enter_kernel)
 		.align	2
 .Ljmp:		.long	start - 0b
 #endif