efi: libstub: Clone memcmp() into the stub

We will no longer be able to call into the kernel image once we merge
the decompressor with the EFI stub, so we need our own implementation of
memcmp(). Let's add the one from lib/string.c and simplify it.

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

5 files changed, 19 insertions, 13 deletions

diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 5a12ca2d7158..f7c8cdf0c302 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -21,7 +21,6 @@ PROVIDE(__efistub_primary_entry_offset	= primary_entry - _text);
  * linked at. The routines below are all implemented in assembler in a
  * position independent manner
  */
-PROVIDE(__efistub_memcmp		= __pi_memcmp);
 PROVIDE(__efistub_memchr		= __pi_memchr);
 PROVIDE(__efistub_strlen		= __pi_strlen);
 PROVIDE(__efistub_strnlen		= __pi_strnlen);
diff --git a/arch/loongarch/kernel/image-vars.h b/arch/loongarch/kernel/image-vars.h
index 88f5d81702df..5b6c7f079942 100644
--- a/arch/loongarch/kernel/image-vars.h
+++ b/arch/loongarch/kernel/image-vars.h
@@ -7,7 +7,6 @@
 
 #ifdef CONFIG_EFI_STUB
 
-__efistub_memcmp		= memcmp;
 __efistub_memchr		= memchr;
 __efistub_strcat		= strcat;
 __efistub_strcmp		= strcmp;
diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
index b46322cb5864..9229cfe0754d 100644
--- a/arch/riscv/kernel/image-vars.h
+++ b/arch/riscv/kernel/image-vars.h
@@ -23,7 +23,6 @@
  * linked at. The routines below are all implemented in assembler in a
  * position independent manner
  */
-__efistub_memcmp		= memcmp;
 __efistub_memchr		= memchr;
 __efistub_strlen		= strlen;
 __efistub_strnlen		= strnlen;
diff --git a/drivers/firmware/efi/libstub/intrinsics.c b/drivers/firmware/efi/libstub/intrinsics.c
index a04ab39292b6..965e734f6f98 100644
--- a/drivers/firmware/efi/libstub/intrinsics.c
+++ b/drivers/firmware/efi/libstub/intrinsics.c
@@ -28,3 +28,21 @@ void *memset(void *dst, int c, size_t len)
 	efi_bs_call(set_mem, dst, len, c & U8_MAX);
 	return dst;
 }
+
+/**
+ * memcmp - Compare two areas of memory
+ * @cs: One area of memory
+ * @ct: Another area of memory
+ * @count: The size of the area.
+ */
+#undef memcmp
+int memcmp(const void *cs, const void *ct, size_t count)
+{
+	const unsigned char *su1, *su2;
+	int res = 0;
+
+	for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
+		if ((res = *su1 - *su2) != 0)
+			break;
+	return res;
+}
diff --git a/drivers/firmware/efi/libstub/zboot.c b/drivers/firmware/efi/libstub/zboot.c
index ea72c8f27da6..38173ec29cd5 100644
--- a/drivers/firmware/efi/libstub/zboot.c
+++ b/drivers/firmware/efi/libstub/zboot.c
@@ -47,15 +47,6 @@ static void error(char *x)
 	log(L"error() called from decompressor library\n");
 }
 
-// Local version to avoid pulling in memcmp()
-static bool guids_eq(const efi_guid_t *a, const efi_guid_t *b)
-{
-	const u32 *l = (u32 *)a;
-	const u32 *r = (u32 *)b;
-
-	return l[0] == r[0] && l[1] == r[1] && l[2] == r[2] && l[3] == r[3];
-}
-
 static efi_status_t __efiapi
 load_file(efi_load_file_protocol_t *this, efi_device_path_protocol_t *rem,
 	  bool boot_policy, unsigned long *bufsize, void *buffer)
@@ -76,7 +67,7 @@ load_file(efi_load_file_protocol_t *this, efi_device_path_protocol_t *rem,
 	if (rem->type == EFI_DEV_MEDIA &&
 	    rem->sub_type == EFI_DEV_MEDIA_VENDOR) {
 		vendor_dp = container_of(rem, struct efi_vendor_dev_path, header);
-		if (!guids_eq(&vendor_dp->vendorguid, &LINUX_EFI_ZBOOT_MEDIA_GUID))
+		if (efi_guidcmp(vendor_dp->vendorguid, LINUX_EFI_ZBOOT_MEDIA_GUID))
 			return EFI_NOT_FOUND;
 
 		decompress = true;