lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 3 Mar 2022 11:09:34 -0800 From: Kees Cook <keescook@...omium.org> To: Dan Li <ashimida@...ux.alibaba.com> Cc: akpm@...ux-foundation.org, arnd@...db.de, catalin.marinas@....com, gregkh@...uxfoundation.org, linux@...ck-us.net, luc.vanoostenryck@...il.com, elver@...gle.com, mark.rutland@....com, masahiroy@...nel.org, ojeda@...nel.org, nathan@...nel.org, npiggin@...il.com, ndesaulniers@...gle.com, samitolvanen@...gle.com, shuah@...nel.org, tglx@...utronix.de, will@...nel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, llvm@...ts.linux.dev, linux-hardening@...r.kernel.org Subject: Re: [PATCH v3 2/2] lkdtm: Add Shadow Call Stack tests On Thu, Mar 03, 2022 at 10:42:45AM -0800, Kees Cook wrote: > Though, having the IS_ENABLED in there makes me wonder if this test > should instead be made _survivable_ on failure. Something like this, > completely untested: > > > #ifdef CONFIG_ARM64 > static noinline void lkdtm_scs_set_lr(unsigned long *addr) > { > unsigned long **lr = (unsigned long **)__builtin_frame_address(0) + 1; > *lr = addr; > } > > /* Function with __noscs attribute clears its return address. */ > static noinline void __noscs lkdtm_noscs_set_lr(unsigned long *addr) > { > unsigned long **lr = (unsigned long **)__builtin_frame_address(0) + 1; > *lr = addr; > } > #endif > > > void lkdtm_CFI_BACKWARD_SHADOW(void) > { > #ifdef CONFIG_ARM64 > > /* Verify the "normal" condition of LR corruption working. */ > do { > /* Keep label in scope to avoid compiler warning. */ > if ((volatile int)0) > goto unexpected; > > pr_info("Trying to corrupt lr in a function without scs protection ...\n"); > lkdtm_noscs_set_lr(&&expected); > > unexpected: > pr_err("XPASS: Unexpectedly survived lr corruption without scs?!\n"); > break; > > expected: > pr_err("ok: lr corruption redirected without scs.\n"); > } while (0); > > > do { > /* Keep labe in scope to avoid compiler warning. */ > if ((volatile int)0) > goto good_scs; > > pr_info("Trying to corrupt lr in a function with scs protection ...\n"); > lkdtm_scs_set_lr(&&bad_scs); > > good_scs: > pr_info("ok: scs takes effect.\n"); > break; > > bad_scs: > pr_err("FAIL: return address rewritten!\n"); > pr_expected_config(CONFIG_SHADOW_CALL_STACK); > } while (0); > #else > pr_err("XFAIL: this test is arm64-only\n"); > #endif > } > > And we should, actually, be able to make the "set_lr" functions be > arch-specific, leaving the test itself arch-agnostic.... Yeah, as a tested example, this works for x86_64, and based on what you had, I'd expect it to work on arm64 too: #include <stdio.h> static __attribute__((noinline)) void set_return_addr(unsigned long *expected, unsigned long *addr) { /* Use of volatile is to make sure final write isn't seen as a dead store. */ unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1; /* Make sure we've found the right place on the stack before writing it. */ if (*ret_addr == expected) *ret_addr = addr; } volatile int force_label; int main(void) { do { /* Keep labels in scope. */ if (force_label) goto normal; if (force_label) goto redirected; set_return_addr(&&normal, &&redirected); normal: printf("I should be skipped\n"); break; redirected: printf("Redirected\n"); } while (0); return 0; } It does _not_ work under Clang, though, which I'm still looking at. -- Kees Cook
Powered by blists - more mailing lists