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Message-ID: <20080517230458.GA18588@damson.getinternet.no>
Date: Sun, 18 May 2008 01:04:58 +0200
From: Vegard Nossum <vegard.nossum@...il.com>
To: Pekka Enberg <penberg@...helsinki.fi>, Ingo Molnar <mingo@...e.hu>,
linux-kernel@...r.kernel.org
Cc: Arjan van de Ven <arjan@...ux.intel.com>,
Andi Kleen <andi@...stfloor.org>
Subject: [PATCH] kmemcheck: support for x86_64
Hi,
Here comes a particularly difficult patch. I am not submitting it for
application to any tree yet, but I have a small hope that somebody will
put their head out to look at it :-)
I am fairly sure the REX handling bits themselves are okay -- the kernel
gets to the point where it tries to mount the root partition. But before
that, there is a torrent of error reports coming from kmemcheck.
Most of them look something like this:
kmemcheck: Caught 8-bit read from freed memory (ffff81000780a904)
ifffffffifffffffifffffffifffffffifffffffifffffffifffffffifffffff
^
and my theory so far is that X86_64 uses some currently unhandled
instruction set extensions like MMX, SSE, etc. (Not 3DNow! because we
have a dependency for that), for a fairly common operation -- something
like memset(), and where we decode the size of the instruction to being
8 bits when in fact it is 64 and thus only mark 8 bits of the shadow
memory as being initialized.
(I guess the easiest way to catch this would be to make cases for those
instructions and WARN(), but... Did I mention I hate this opcode decoding
business? It's just too ugly.)
Do the #ifdef X86_64 parts look okay?
The patch applies to the 'current' branch of kmemcheck.git:
http://git.kernel.org/?p=linux/kernel/git/vegard/kmemcheck.git;a=shortlog;h=current
Note: kmemcheck reports from x86_64 are still not very good because of the
stacktrace issues reported earlier; in short, we can't look further than
the page fault stack entry, which makes it rather useless for debugging.
We do still have the RIP of the crash, though. End of note.
Thanks.
Vegard
>From d7978af9df6e61b75f1d15a65cf455b89aafea08 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@...il.com>
Date: Sun, 11 May 2008 14:06:49 +0200
Subject: [PATCH] kmemcheck: support for x86_64
Add REX prefix handling to kmemcheck's opcode decoder.
Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>
---
arch/x86/Kconfig.debug | 2 +-
arch/x86/kernel/kmemcheck.c | 67 ++++++++++++++++++++++++++++++++++--------
2 files changed, 55 insertions(+), 14 deletions(-)
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index af6c1b3..8f02410 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -244,7 +244,7 @@ endif
config KMEMCHECK
bool "kmemcheck: trap use of uninitialized memory"
- depends on X86_32
+ depends on X86
depends on !X86_USE_3DNOW
depends on SLUB || SLAB
depends on !CC_OPTIMIZE_FOR_SIZE
diff --git a/arch/x86/kernel/kmemcheck.c b/arch/x86/kernel/kmemcheck.c
index 80ef428..bd52609 100644
--- a/arch/x86/kernel/kmemcheck.c
+++ b/arch/x86/kernel/kmemcheck.c
@@ -600,6 +600,12 @@ opcode_is_prefix(uint8_t b)
|| b == 0x67;
}
+static bool
+opcode_is_rex_prefix(uint8_t b)
+{
+ return (b & 0xf0) == 0x40;
+}
+
/* This is a VERY crude opcode decoder. We only need to find the size of the
* load/store that caused our #PF and this should work for all the opcodes
* that we care about. Moreover, the ones who invented this instruction set
@@ -616,6 +622,15 @@ opcode_get_size(const uint8_t *op)
operand_size_override = 16;
}
+#ifdef X86_64
+ /* REX prefix */
+ if (opcode_is_rex_prefix(*op)) {
+ if (*op & 0x08)
+ return 64;
+ ++op;
+ }
+#endif
+
/* escape opcode */
if (*op == 0x0f) {
++op;
@@ -633,7 +648,10 @@ static const uint8_t *
opcode_get_primary(const uint8_t *op)
{
/* skip prefixes */
- for (; opcode_is_prefix(*op); ++op);
+ while (opcode_is_prefix(*op))
+ ++op;
+ if (opcode_is_rex_prefix(*op))
+ ++op;
return op;
}
@@ -644,22 +662,16 @@ opcode_get_primary(const uint8_t *op)
static bool
check_page_boundary(struct pt_regs *regs, unsigned long addr, unsigned int size)
{
- unsigned long page[4];
-
if (size == 8)
return false;
-
- page[0] = (addr + 0) & PAGE_MASK;
- page[1] = (addr + 1) & PAGE_MASK;
-
- if (size == 16 && page[0] == page[1])
+ if (size == 16 && (addr & PAGE_MASK) == ((addr + 1) & PAGE_MASK))
return false;
-
- page[2] = (addr + 2) & PAGE_MASK;
- page[3] = (addr + 3) & PAGE_MASK;
-
- if (size == 32 && page[0] == page[2] && page[0] == page[3])
+ if (size == 32 && (addr & PAGE_MASK) == ((addr + 3) & PAGE_MASK))
return false;
+#ifdef X86_64
+ if (size == 64 && (addr & PAGE_MASK) == ((addr + 7) & PAGE_MASK))
+ return false;
+#endif
/*
* XXX: The addr/size data is also really interesting if this
@@ -683,6 +695,17 @@ test(void *shadow, unsigned int size)
* code to access neighboring bytes.
*/
switch (size) {
+#ifdef X86_64
+ case 64:
+ if (x[7] == SHADOW_INITIALIZED)
+ return x[7];
+ if (x[6] == SHADOW_INITIALIZED)
+ return x[6];
+ if (x[5] == SHADOW_INITIALIZED)
+ return x[5];
+ if (x[4] == SHADOW_INITIALIZED)
+ return x[4];
+#endif
case 32:
if (x[3] == SHADOW_INITIALIZED)
return x[3];
@@ -697,6 +720,17 @@ test(void *shadow, unsigned int size)
}
#else
switch (size) {
+#ifdef X86_64
+ case 64:
+ if (x[7] != SHADOW_INITIALIZED)
+ return x[7];
+ if (x[6] != SHADOW_INITIALIZED)
+ return x[6];
+ if (x[5] != SHADOW_INITIALIZED)
+ return x[5];
+ if (x[4] != SHADOW_INITIALIZED)
+ return x[4];
+#endif
case 32:
if (x[3] != SHADOW_INITIALIZED)
return x[3];
@@ -722,6 +756,13 @@ set(void *shadow, unsigned int size)
x = shadow;
switch (size) {
+#ifdef X86_64
+ case 64:
+ x[7] = SHADOW_INITIALIZED;
+ x[6] = SHADOW_INITIALIZED;
+ x[5] = SHADOW_INITIALIZED;
+ x[4] = SHADOW_INITIALIZED;
+#endif
case 32:
x[3] = SHADOW_INITIALIZED;
x[2] = SHADOW_INITIALIZED;
--
1.5.4.1
--
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