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 linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 4 Mar 2022 06:54:23 -0800 From: Dan Li <ashimida@...ux.alibaba.com> To: Kees Cook <keescook@...omium.org> 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 3/3/22 11:09, Kees Cook wrote: > 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: >> >> >> 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; From the assembly code, it seems that "&&normal" does't always equal to the address of label "normal" when we use clang with -O2. > redirected: > printf("Redirected\n"); > } while (0); > The address of "&&redirected" may appear in the middle of the assembly instructions of the printf. If we unconditionally jump to "&&normal", it may crash directly because x0 is not set correctly. > return 0; > } > > > It does _not_ work under Clang, though, which I'm still looking at. > AFAICT, maybe we could specify -O0 optimization to bypass this. BTW: Occasionally found, the following code works correctly, but i think it doesn't solve the issue :) #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"); printf("\n"); //add a new printf } while (0); return 0; }
Powered by blists - more mailing lists