The patch titled
i386: let usermode execute the "enter" instruction
has been added to the -mm tree. Its filename is
i386-let-usermode-execute-the-enter.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
From: Chuck Ebbert <76306.1226@xxxxxxxxxxxxxx>
The i386 page fault handler does not allow enough slack when checking for
userspace access below the current stack pointer. This prevents use of the
enter instruction by user code. Fix this by allowing enough slack for
"enter $65535,$31" to execute.
Problem reported by Tomasz Malesinski <tmal@xxxxxxxxxxxx>
Tested using this program, based on the original from Tomasz:
.file "ovflow.S"
.version "01.01"
gcc2_compiled.:
.section .rodata
.LC0:
.string "asdf\n"
.text
.align 4
.globl main
.type main,@function
main:
nest_level=0
.rept 30
enter $0,$nest_level
nest_level=nest_level+1
.endr
enter $65535,$30
enter $65535,$31
addl $-12,%esp
pushl $.LC0
call printf
addl $16,%esp
.L2:
.rept 32
leave
.endr
ret
.Lfe1:
.size main,.Lfe1-main
.ident "GCC: (GNU) 2.95.4 20011002 (Debian prerelease)"
Signed-off-by: Chuck Ebbert <76306.1226@xxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
arch/i386/mm/fault.c | 10 +++++-----
1 files changed, 5 insertions(+), 5 deletions(-)
diff -puN arch/i386/mm/fault.c~i386-let-usermode-execute-the-enter arch/i386/mm/fault.c
--- devel/arch/i386/mm/fault.c~i386-let-usermode-execute-the-enter 2006-05-18 01:29:58.000000000 -0700
+++ devel-akpm/arch/i386/mm/fault.c 2006-05-18 01:29:58.000000000 -0700
@@ -380,12 +380,12 @@ fastcall void __kprobes do_page_fault(st
goto bad_area;
if (error_code & 4) {
/*
- * accessing the stack below %esp is always a bug.
- * The "+ 32" is there due to some instructions (like
- * pusha) doing post-decrement on the stack and that
- * doesn't show up until later..
+ * Accessing the stack below %esp is always a bug.
+ * The large cushion allows instructions like enter
+ * and pusha to work. ("enter $65535,$31" pushes
+ * 32 pointers and then decrements %esp by 65535.)
*/
- if (address + 32 < regs->esp)
+ if (address + 65536 + 32 * sizeof(unsigned long) < regs->esp)
goto bad_area;
}
if (expand_stack(vma, address))
_
Patches currently in -mm which might be from 76306.1226@xxxxxxxxxxxxxx are
i386-remove-junk-from-stack-dump.patch
i386-let-usermode-execute-the-enter.patch
-
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