lkml.org 
[lkml]   [2005]   [Apr]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[patch 010/198] fix crash in entry.S restore_all
From
Date

From: Stas Sergeev <stsp@aknet.ru>

Fix the access-above-bottom-of-stack crash.

1. Allows to preserve the valueable optimization

2. Works for NMIs

3. Doesn't care whether or not there are more of the like instances
where the stack is left empty.

4. Seems to work for me without the crashes:)

(akpm: this is still under discussion, although I _think_ it's OK. You might
want to hold off)

Signed-off-by: Stas Sergeev <stsp@aknet.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

25-akpm/arch/i386/kernel/entry.S | 3 +++
25-akpm/arch/i386/kernel/process.c | 12 +++++++++++-
2 files changed, 14 insertions(+), 1 deletion(-)

diff -puN arch/i386/kernel/process.c~fix-crash-in-entrys-restore_all arch/i386/kernel/process.c
--- 25/arch/i386/kernel/process.c~fix-crash-in-entrys-restore_all 2005-04-12 03:21:05.840249048 -0700
+++ 25-akpm/arch/i386/kernel/process.c 2005-04-12 03:21:05.845248288 -0700
@@ -405,7 +405,17 @@ int copy_thread(int nr, unsigned long cl
childregs->esp = esp;

p->thread.esp = (unsigned long) childregs;
- p->thread.esp0 = (unsigned long) (childregs+1);
+ /*
+ * The below -8 is to reserve 8 bytes on top of the ring0 stack.
+ * This is necessary to guarantee that the entire "struct pt_regs"
+ * is accessable even if the CPU haven't stored the SS/ESP registers
+ * on the stack (interrupt gate does not save these registers
+ * when switching to the same priv ring).
+ * Therefore beware: accessing the xss/esp fields of the
+ * "struct pt_regs" is possible, but they may contain the
+ * completely wrong values.
+ */
+ p->thread.esp0 = (unsigned long) (childregs+1) - 8;

p->thread.eip = (unsigned long) ret_from_fork;

diff -puN arch/i386/kernel/entry.S~fix-crash-in-entrys-restore_all arch/i386/kernel/entry.S
--- 25/arch/i386/kernel/entry.S~fix-crash-in-entrys-restore_all 2005-04-12 03:21:05.841248896 -0700
+++ 25-akpm/arch/i386/kernel/entry.S 2005-04-12 03:21:05.846248136 -0700
@@ -245,6 +245,9 @@ syscall_exit:

restore_all:
movl EFLAGS(%esp), %eax # mix EFLAGS, SS and CS
+ # Warning: OLDSS(%esp) contains the wrong/random values if we
+ # are returning to the kernel.
+ # See comments in process.c:copy_thread() for details.
movb OLDSS(%esp), %ah
movb CS(%esp), %al
andl $(VM_MASK | (4 << 8) | 3), %eax
_
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2005-04-12 20:27    [W:0.023 / U:0.228 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site