Jeremy Fitzhardinge wrote:
Well, in the Xen case, where the pages are simply not mapped, then
the signature simply won't exist. In other cases, I guess its
possible the signature might exist but the rest of the ROM doesn't,
but that won't happen on normal hardware.
In your opinion, is the attached (versus 2.6.20-rc3) better? This uses
probe_kernel_address() for all accesses. Or rather, an expanded version
thereof. The set_fs() and pagefault_{disable,enable} calls are only done
once in probe_roms().
Accessing the length byte at rom[2] with __get_user() is overkill after
just checking the signature at 0 and 1 but direcly accessing only that
makes for inconsistent code IMO. It's only a .fixup entry...
I can't say I'm all that sure that that pagefault_disable() call is
still applicable now that it got expanded into the probe_roms() stage?
Rene.
commit f153a588097c08cefdb799f22123192a9975d273
Author: Rene Herman <[email protected]>
Date: Sat Jan 6 04:09:32 2007 +0100
Use __get_user() for ISA ROM accesses.
In virtualized environments, the ISA ROMs may not be mapped so be careful
about touching them.
Signed-off-by: Rene Herman <[email protected]>
diff --git a/arch/i386/kernel/e820.c b/arch/i386/kernel/e820.c
index f391abc..8b54f65 100644
--- a/arch/i386/kernel/e820.c
+++ b/arch/i386/kernel/e820.c
@@ -156,29 +156,34 @@ static struct resource standard_io_resou
.flags = IORESOURCE_BUSY | IORESOURCE_IO
} };
-static int romsignature(const unsigned char *x)
+#define ROM_SIG 0xaa55
+
+static int __init romsignature(const unsigned char *rom)
{
unsigned short sig;
- int ret = 0;
- if (probe_kernel_address((const unsigned short *)x, sig) == 0)
- ret = (sig == 0xaa55);
- return ret;
+
+ return !__get_user(sig, (const unsigned short *)rom) && sig == ROM_SIG;
}
-static int __init romchecksum(unsigned char *rom, unsigned long length)
+static int __init romchecksum(const unsigned char *rom, unsigned long length)
{
- unsigned char *p, sum = 0;
+ unsigned char sum, c;
- for (p = rom; p < rom + length; p++)
- sum += *p;
- return sum == 0;
+ for (sum = 0; length && !__get_user(c, rom); rom++, length--)
+ sum += c;
+ return !length && !sum;
}
static void __init probe_roms(void)
{
+ const unsigned char *rom;
unsigned long start, length, upper;
- unsigned char *rom;
- int i;
+ unsigned char c;
+ int i;
+ mm_segment_t old_fs = get_fs();
+
+ set_fs(KERNEL_DS);
+ pagefault_disable();
/* video rom */
upper = adapter_rom_resources[0].start;
@@ -189,8 +194,11 @@ static void __init probe_roms(void)
video_rom_resource.start = start;
+ if (__get_user(c, rom + 2))
+ continue;
+
/* 0 < length <= 0x7f * 512, historically */
- length = rom[2] * 512;
+ length = c * 512;
/* if checksum okay, trust length byte */
if (length && romchecksum(rom, length))
@@ -224,8 +232,11 @@ static void __init probe_roms(void)
if (!romsignature(rom))
continue;
+ if (__get_user(c, rom + 2))
+ continue;
+
/* 0 < length <= 0x7f * 512, historically */
- length = rom[2] * 512;
+ length = c * 512;
/* but accept any length that fits if checksum okay */
if (!length || start + length > upper || !romchecksum(rom, length))
@@ -237,6 +248,9 @@ static void __init probe_roms(void)
start = adapter_rom_resources[i++].end & ~2047UL;
}
+
+ pagefault_enable();
+ set_fs(old_fs);
}
/*
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