diff options
| -rw-r--r-- | src/interface/efi/efi_init.c | 23 |
1 files changed, 17 insertions, 6 deletions
diff --git a/src/interface/efi/efi_init.c b/src/interface/efi/efi_init.c index df46bb17b..284c39b35 100644 --- a/src/interface/efi/efi_init.c +++ b/src/interface/efi/efi_init.c @@ -22,6 +22,7 @@ FILE_LICENCE ( GPL2_OR_LATER ); #include <string.h> #include <errno.h> #include <ipxe/init.h> +#include <ipxe/rotate.h> #include <ipxe/efi/efi.h> #include <ipxe/efi/efi_driver.h> #include <ipxe/efi/Protocol/LoadedImage.h> @@ -105,19 +106,29 @@ static void * efi_find_table ( EFI_GUID *guid ) { */ __attribute__ (( noinline )) unsigned long efi_stack_cookie ( EFI_HANDLE handle ) { + unsigned long cookie = 0; + unsigned int rotation = ( 8 * sizeof ( cookie ) / 4 ); /* There is no viable source of entropy available at this * point. Construct a value that is at least likely to vary * between platforms and invocations. - * - * Ensure that the value contains a NUL byte, to act as a + */ + cookie ^= ( ( unsigned long ) handle ); + cookie = roll ( cookie, rotation ); + cookie ^= ( ( unsigned long ) &handle ); + cookie = roll ( cookie, rotation ); + cookie ^= profile_timestamp(); + cookie = roll ( cookie, rotation ); + cookie ^= build_id; + + /* Ensure that the value contains a NUL byte, to act as a * runaway string terminator. Construct the NUL using a shift * rather than a mask, to avoid losing valuable entropy in the - * low-order bits. + * lower-order bits. */ - return ( ( ( ( unsigned long ) handle ) ^ - ( ( unsigned long ) &handle ) ^ - profile_timestamp() ^ build_id ) << 8 ); + cookie <<= 8; + + return cookie; } /** |