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authorChuck Ebbert <76306.1226@compuserve.com>2006-06-23 02:04:23 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-23 07:42:57 -0700
commit21528454f6dd18231ae20102f98aa8f51b6ec1b9 (patch)
treea167603f42c51c0e1a731ae9629305a11a5b8e44 /arch
parent1b61b910e99059abdd54c93aa70e84e076e33d16 (diff)
[PATCH] i386: let usermode execute the "enter" instruction
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@mimuw.edu.pl> 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@compuserve.com> Cc: Andi Kleen <ak@muc.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/i386/mm/fault.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
index 7f0fcf219a2..f38085ff3c3 100644
--- a/arch/i386/mm/fault.c
+++ b/arch/i386/mm/fault.c
@@ -380,12 +380,12 @@ fastcall void __kprobes do_page_fault(struct pt_regs *regs,
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))