[PATCH] efi/zboot: Avoid CopyMem/SetMem EFI services after ExitBootServices

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

Given that memset/memcpy are intrinsics, the compiler might insert calls
to these routines unpredictably, including in code that executes after
ExitBootServices(). In this case, the respective boot services are no
longer accessible, and calling them will cause a crash.

So detect this case, and fall back to a bytewise copy/store if it occurs.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/libstub/intrinsics.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/libstub/intrinsics.c b/drivers/firmware/efi/libstub/intrinsics.c
index 965e734f6f98..f26c19cf65fb 100644
--- a/drivers/firmware/efi/libstub/intrinsics.c
+++ b/drivers/firmware/efi/libstub/intrinsics.c
@@ -17,7 +17,12 @@ void *__memset(void *s, int c, size_t count) __alias(memset);
 
 void *memcpy(void *dst, const void *src, size_t len)
 {
-	efi_bs_call(copy_mem, dst, src, len);
+	if (efi_table_attr(efi_system_table, boottime) != NULL)
+		efi_bs_call(copy_mem, dst, src, len);
+	else
+		for (size_t i = 0; i < len; i++)
+			((u8 *)dst)[i] = ((u8 *)src)[i];
+
 	return dst;
 }
 
@@ -25,7 +30,12 @@ extern void *memmove(void *dst, const void *src, size_t len) __alias(memcpy);
 
 void *memset(void *dst, int c, size_t len)
 {
-	efi_bs_call(set_mem, dst, len, c & U8_MAX);
+	if (efi_table_attr(efi_system_table, boottime) != NULL)
+		efi_bs_call(set_mem, dst, len, c & U8_MAX);
+	else
+		for (u8 *d = dst; len--; d++)
+			*d = c;
+
 	return dst;
 }
 
-- 
2.48.1.658.g4767266eb4-goog