[libc-commits] [libc] [libc] fortify jmp buffer for x86-64 (PR #112769)

[Nick Desaulniers via libc-commits]

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@@ -8,35 +8,83 @@
 
 #include "src/setjmp/longjmp.h"
 #include "include/llvm-libc-macros/offsetof-macro.h"
+#include "src/__support/OSUtil/io.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
+#include "src/setjmp/checksum.h"
+#include "src/stdlib/abort.h"
 
 #if !defined(LIBC_TARGET_ARCH_IS_X86_64)
 #error "Invalid file include"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {
 
+#if LIBC_COPT_SETJMP_ENABLE_FORTIFICATION
+extern "C" [[gnu::cold, noreturn]] void __libc_jmpbuf_corruption() {
+  write_to_stderr("invalid checksum detected in longjmp\n");
+  abort();
+}
+#define LOAD_CHKSUM_STATE_REGISTERS()                                          \
+  asm("mov %0, %%rcx\n\t" ::"m"(jmpbuf::value_mask) : "rcx");                  \
+  asm("mov %0, %%rdx\n\t" ::"m"(jmpbuf::checksum_cookie) : "rdx");
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nickdesaulniers wrote:

It's probably better to load the value_mask and checksum_cookie in one asm block. As is, this is hoping that the value placed in rcx by the first asm block and rdx by the second remains by the third.  There are no such guarantees provided.

https://github.com/llvm/llvm-project/pull/112769