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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Windows stack guard needs to XOR the stack pointer with __stack_cookie"
href="https://bugs.llvm.org/show_bug.cgi?id=35449">35449</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Windows stack guard needs to XOR the stack pointer with __stack_cookie
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>rnk@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Consider:
void g(int*);
void f() {
int x[16];
g(&x[0]);
}
Compiled like so, here is a comparison of the relevant code:
$ cl -O2 -GS t2.c -Fat.s -c && grep -B1 -A2 security t.s
...
sub rsp, 120 ; 00000078H
mov rax, QWORD PTR __security_cookie
xor rax, rsp
mov QWORD PTR __$ArrayPad$[rsp], rax
--
xor rcx, rsp
call __security_check_cookie
add rsp, 120 ; 00000078H
ret 0
$ clang-cl -O2 -GS t2.c -Fat.s -c && grep -B1 -A2 security t.s
.seh_endprologue
movq __security_cookie(%rip), %rax
movq %rax, 96(%rsp)
leaq 32(%rsp), %rcx
--
movq 96(%rsp), %rcx
callq __security_check_cookie
nop
addq $104, %rsp
The same is done with EBP on 32-bit. XORing the stack pointer (or frame pointer
when appropriate) into the canary improves security by making it harder to a
valid cookie from one location to another to bypass the guard.</pre>
</div>
</p>
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