x86 setup: fix ghost entries under /sys/firmware/edd take 3
Some BIOSes do not indicate error when trying to read from non-
existing device. Zero buffer before reading and check that we
possibly have valid MBR by looking for MBR magic.
This was fixed in different way for edd.S in
http://marc.info/?l=linux-kernel&m=114087765422490&w=2, but lost
again when edd.S was rewritten in C.
Signed-off-by: Andrey Borzenkov < arvidjaar@mail.ru>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/boot/edd.c b/arch/x86/boot/edd.c
index bf4ae6f..067e28c 100644
--- a/arch/x86/boot/edd.c
+++ b/arch/x86/boot/edd.c
@@ -43,6 +43,7 @@
char *mbrbuf_ptr, *mbrbuf_end;
u32 buf_base, mbr_base;
extern char _end[];
+ u16 mbr_magic;
sector_size = ei->params.bytes_per_sector;
if (!sector_size)
@@ -60,11 +61,15 @@
if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
return -1;
+ memset(mbrbuf_ptr, 0, sector_size);
if (read_mbr(devno, mbrbuf_ptr))
return -1;
*mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
- return 0;
+ mbr_magic = *(u16 *)&mbrbuf_ptr[510];
+
+ /* check for valid MBR magic */
+ return mbr_magic == 0xAA55 ? 0 : -1;
}
static int get_edd_info(u8 devno, struct edd_info *ei)