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, 17 insertions, 69 deletions

diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
index 304d5b02ca67..4cfd03c35c49 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -10,81 +10,35 @@
 
 #include <asm/assembler.h>
 
-#define EFI_LOAD_ERROR 0x8000000000000001
-
 	__INIT
 
-	/*
-	 * We arrive here from the EFI boot manager with:
-	 *
-	 *    * CPU in little-endian mode
-	 *    * MMU on with identity-mapped RAM
-	 *    * Icache and Dcache on
-	 *
-	 * We will most likely be running from some place other than where
-	 * we want to be. The kernel image wants to be placed at TEXT_OFFSET
-	 * from start of RAM.
-	 */
-ENTRY(entry)
-	/*
-	 * Create a stack frame to save FP/LR with extra space
-	 * for image_addr variable passed to efi_entry().
-	 */
-	stp	x29, x30, [sp, #-32]!
-	mov	x29, sp
-
-	/*
-	 * Call efi_entry to do the real work.
-	 * x0 and x1 are already set up by firmware. Current runtime
-	 * address of image is calculated and passed via *image_addr.
-	 *
-	 * unsigned long efi_entry(void *handle,
-	 *                         efi_system_table_t *sys_table,
-	 *                         unsigned long *image_addr) ;
-	 */
-	adr_l	x8, _text
-	add	x2, sp, 16
-	str	x8, [x2]
-	bl	efi_entry
-	cmn	x0, #1
-	b.eq	efi_load_fail
-
+ENTRY(efi_enter_kernel)
 	/*
 	 * efi_entry() will have copied the kernel image if necessary and we
-	 * return here with device tree address in x0 and the kernel entry
-	 * point stored at *image_addr. Save those values in registers which
-	 * are callee preserved.
-	 */
-	mov	x20, x0		// DTB address
-	ldr	x0, [sp, #16]	// relocated _text address
-	ldr	w21, =stext_offset
-	add	x21, x0, x21
-
-	/*
-	 * Calculate size of the kernel Image (same for original and copy).
+	 * end up here with device tree address in x1 and the kernel entry
+	 * point stored in x0. Save those values in registers which are
+	 * callee preserved.
 	 */
-	adr_l	x1, _text
-	adr_l	x2, _edata
-	sub	x1, x2, x1
+	mov	x19, x0			// relocated Image address
+	mov	x20, x1			// DTB address
 
 	/*
 	 * Flush the copied Image to the PoC, and ensure it is not shadowed by
 	 * stale icache entries from before relocation.
 	 */
+	ldr	w1, =kernel_size
 	bl	__flush_dcache_area
 	ic	ialluis
+	dsb	sy
 
 	/*
-	 * Ensure that the rest of this function (in the original Image) is
-	 * visible when the caches are disabled. The I-cache can't have stale
-	 * entries for the VA range of the current image, so no maintenance is
-	 * necessary.
+	 * Jump across, into the copy of the image that we just cleaned
+	 * to the PoC, so that we can safely disable the MMU and caches.
 	 */
-	adr	x0, entry
-	adr	x1, entry_end
-	sub	x1, x1, x0
-	bl	__flush_dcache_area
-
+	ldr	w0, .Ljmp
+	sub	x0, x19, w0, sxtw
+	br	x0
+0:
 	/* Turn off Dcache and MMU */
 	mrs	x0, CurrentEL
 	cmp	x0, #CurrentEL_EL2
@@ -109,12 +63,6 @@ ENTRY(entry)
 	mov	x1, xzr
 	mov	x2, xzr
 	mov	x3, xzr
-	br	x21
-
-efi_load_fail:
-	mov	x0, #EFI_LOAD_ERROR
-	ldp	x29, x30, [sp], #32
-	ret
-
-entry_end:
-ENDPROC(entry)
+	b	stext
+ENDPROC(efi_enter_kernel)
+.Ljmp:	.long	_text - 0b