* Re: + x86-fix-ghost-entries-under-sys-firmware-edd.patch added to -mm tree
[not found] <200810030634.m936YVDC014640@imap1.linux-foundation.org>
@ 2008-10-03 17:08 ` Andrey Borzenkov
2008-10-03 17:15 ` H. Peter Anvin
0 siblings, 1 reply; 2+ messages in thread
From: Andrey Borzenkov @ 2008-10-03 17:08 UTC (permalink / raw)
To: akpm; +Cc: Linux Kernel Mailing List, Matt_Domsch, hpa, mingo, tglx
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On Friday 03 October 2008, akpm@linux-foundation.org wrote:
> hpa:
>
> Right, I think that's a much better patch.
>
> The really Right Thing[TM] to do is probably to pre-clear the buffer
> and then look for the 0xaa55 signature at offset 510; it is required
> for sector 0 to be a valid MBR-format partition table and hence for the
> MBR *signature* to be valid.
>
> I'll write that up tomorrow (I'm travelling today), or you can send
> me a patch.
>
> akpm:
>
> A patch in hand is worth...
I am really sorry; I botched this initially and then was distracted by other
things. The patch attached.
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Subject: [PATCH] Fix ghost entries under /sys/firmware/edd take 3
From: Andrey Borzenkov < arvidjaar@mail.ru>
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>
---
arch/x86/boot/edd.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/arch/x86/boot/edd.c b/arch/x86/boot/edd.c
index d93cbc6..1aae8f3 100644
--- a/arch/x86/boot/edd.c
+++ b/arch/x86/boot/edd.c
@@ -41,6 +41,7 @@ static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
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)
@@ -58,11 +59,15 @@ static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
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)
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