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

[Nick Desaulniers via libc-commits]

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@@ -103,6 +103,10 @@
     "LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER": {
       "value": true,
       "doc": "Make setjmp save the value of x18, and longjmp restore it. The AArch64 ABI delegates this register to platform ABIs, which can choose whether to make it caller-saved."
+    },
+    "LIBC_CONF_SETJMP_FORTIFICATION": {
+      "value": false,
+      "doc": "Protect jmp_buf by masking its contents and storing a simple checksum, to make it harder for an attacker to read meaningful information from a jmp_buf or to modify it. This is only supported on x86-64 Linux."
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nickdesaulniers wrote:

We will eventually need to support shadow stacks (part of Intel's CET): https://libc-alpha.sourceware.narkive.com/KcCIyBg9/patch-linux-x86-support-shadow-stack-pointer-in-setjmp-longjmp.  It's perhaps worth discussing if we'll want to have 2 or 3 configs for fortification.

For instance, I'd imaging we'd want full fortification or no fortification.  But I wonder if shadow stacks make checksumming irrelevant? Hmm...I'll need to think about that more.

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