181519cf38
11b3a0c2c5db115412c37195#explicit zero 1131456ac632#brk 1158ebc243ea#random 115323b39f7e#undefined 116a91d9dddb#merge 11a042b5a0ba#vla formatting 119ec639de1b#pthread 1149571a0a49#read only 11149cc5ccb8#zero 112e613ccbe7#fork mmap 11e239c7dff8#memprot pthread 110b03d92b7f#xor 11de08419b82#junk 11897d4903e2#guard 11648cd68ca3#ptrhread guard 110bc4dbcbd2#stack rand 10aa9cc05d0710a8cdbb6352#explicit zero 10b28302c668#brk 109f8be7d07c#random 10cb91a7ee3a#undefined 1008279e2fdd#merge 106a18bd565d#vla formatting 102f392c2d08#pthread 108bbce1bc50#read only 10725f61db82#zero 104cd257135f#fork mmap 109220cf622b#memprot pthread 108ef71d1ffd#memprot exit 100eaef1abbd#xor 1064f1cc2148#junk 105c42a527cf#guard 105cc8c34e60#pthread guard 107f61cc8a1c#stack rand 9abdf523d269e4b9b31e6f#explicit zero 9a3a22a63d2#brk 97444dbc3cf#random 9dcd3b72ac9#undefined 9543e1df342#merge 9611e5691f7#vla formatting 98de97ce864#pthread 9a475717042#read only 97f0947cc0e#zero 9e9751d3370#fork mmap 983cd86d0d5#memprot pthread 91ebb165455#memprot exit 9488ba483cf#xor 9f9351d884b#junk 985e5bca0a5#move Signed-off-by: Tad <tad@spotco.us>
35 lines
1.4 KiB
Diff
35 lines
1.4 KiB
Diff
From 7f0947cc0e4fc52a41ef8ecfba892f5534e1fee5 Mon Sep 17 00:00:00 2001
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From: Daniel Micay <danielmicay@gmail.com>
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Date: Sun, 12 Mar 2017 17:49:13 -0400
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Subject: [PATCH] on 64-bit, zero the leading stack canary byte
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This reduces entropy of the canary from 64-bit to 56-bit in exchange for
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mitigating non-terminated C string overflows.
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---
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libc/bionic/__libc_init_main_thread.cpp | 10 ++++++++++
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1 file changed, 10 insertions(+)
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diff --git a/libc/bionic/__libc_init_main_thread.cpp b/libc/bionic/__libc_init_main_thread.cpp
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index 78d25fd977..ae2245829d 100644
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--- a/libc/bionic/__libc_init_main_thread.cpp
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+++ b/libc/bionic/__libc_init_main_thread.cpp
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@@ -47,8 +47,18 @@ extern "C" int __set_tid_address(int* tid_address);
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__attribute__((aligned(PAGE_SIZE)))
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uintptr_t __stack_chk_guard[PAGE_SIZE / sizeof(uintptr_t)] = {0};
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+#if __LP64__
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+static const uintptr_t canary_mask = __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ ?
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+ 0xffffffffffffff00UL :
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+ 0x00ffffffffffffffUL;
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+#endif
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+
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void __libc_init_global_stack_chk_guard(KernelArgumentBlock& args) {
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__libc_safe_arc4random_buf(&__stack_chk_guard[0], sizeof(__stack_chk_guard[0]), args);
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+#if __LP64__
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+ // Sacrifice 8 bits of entropy on 64-bit to mitigate non-terminated C string overflows
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+ __stack_chk_guard[0] &= canary_mask;
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+#endif
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if (mprotect(__stack_chk_guard, sizeof(__stack_chk_guard), PROT_READ) == -1) {
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async_safe_fatal("mprotect __stack_chk_guard: %s", strerror(errno));
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}
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