<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Safe-stack leaks stack with dynamic alloca"
href="https://llvm.org/bugs/show_bug.cgi?id=26122">26122</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Safe-stack leaks stack with dynamic alloca
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Miscellaneous Instrumentation passes
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kuba.brecka@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Safe-stack instrumentation seems to wrongly handle some dynamic alloca cases.
Here's a test case that crashes when -fsanitize=safe-stack is used on it. We
seem to forget to reset the unsafe stack pointer when leaving the function,
causing a stack leak and eventually overrunning the unsafe stack.
#include <alloca.h>
#include <stdio.h>
void f() {
for (int i = 0; i < 10; i++) {
int *p = alloca(4096);
*p = 42;
}
}
int main(int argc, const char * argv[]) {
printf("Hello, World!\n");
for (int i = 0; i < 10000000; i++) {
f();
}
return 0;
}
Disassembly:
f:
0x100000ed0 <+0>: pushq %rbp
0x100000ed1 <+1>: movq %rsp, %rbp
0x100000ed4 <+4>: movl $0x0, -0x4(%rbp)
0x100000edb <+11>: cmpl $0xa, -0x4(%rbp)
0x100000edf <+15>: jge 0x100000f1d ; <+77> at
safe-stack-alloca-crash.c:9
0x100000ee5 <+21>: movq %gs:0x80, %rax
0x100000eee <+30>: addq $-0x1000, %rax
0x100000ef4 <+36>: andq $-0x10, %rax
0x100000ef8 <+40>: movq %rax, %gs:0x80
0x100000f01 <+49>: movq %rax, -0x10(%rbp)
0x100000f05 <+53>: movq -0x10(%rbp), %rax
0x100000f09 <+57>: movl $0x2a, (%rax)
0x100000f0f <+63>: movl -0x4(%rbp), %eax
0x100000f12 <+66>: addl $0x1, %eax
0x100000f15 <+69>: movl %eax, -0x4(%rbp)
0x100000f18 <+72>: jmp 0x100000edb ; <+11> at
safe-stack-alloca-crash.c:5
0x100000f1d <+77>: popq %rbp
0x100000f1e <+78>: retq</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>