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Add comments and unify guard page setup.

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While currently only NetBSD seems to be affected, all systems
implementing PAX MPROTECT in strict mode need this treatment,
and it does not hurt others.
This commit is contained in:
Martin Husemann 2018-05-02 10:00:33 +02:00
parent 7c2304ddc6
commit 244e24a312
1 changed files with 13 additions and 16 deletions
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29
src/libstd/sys/unix/thread.rs
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@ -326,23 +326,20 @@ pub mod guard {
// Reallocate the last page of the stack.
// This ensures SIGBUS will be raised on
// stack overflow.
if cfg!(target_os = "netbsd") {
let result = mmap(stackaddr, PAGE_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
if result != stackaddr || result == MAP_FAILED {
panic!("failed to allocate a guard page");
}
let result = mprotect(stackaddr, PAGE_SIZE, 0);
// Systems which enforce strict PAX MPROTECT do not allow
// to mprotect() a mapping with less restrictive permissions
// than the initial mmap() used, so we mmap() here with
// read/write permissions and only then mprotect() it to
// no permissions at all. See issue #50313.
let result = mmap(stackaddr, PAGE_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
if result != stackaddr || result == MAP_FAILED {
panic!("failed to allocate a guard page");
}
if result != 0 {
panic!("unable to protect the guard page");
}
} else {
let result = mmap(stackaddr, PAGE_SIZE, PROT_NONE,
MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
if result != stackaddr || result == MAP_FAILED {
panic!("failed to allocate a guard page");
}
let result = mprotect(stackaddr, PAGE_SIZE, PROT_NONE);
if result != 0 {
panic!("failed to protect the guard page");
}
let guardaddr = stackaddr as usize;