| 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
| ||
|
Message-ID: <CAP045ApfQnsHsimmhLsSeL2OSB98-Q3f=nM4em5rqr_paz4=5Q@mail.gmail.com>
Date: Wed, 19 Aug 2020 12:28:16 -0700
From: Kyle Huey <me@...ehuey.com>
To: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
Andy Lutomirski <luto@...nel.org>,
"Robert O'Callahan" <rocallahan@...il.com>,
LKML <linux-kernel@...r.kernel.org>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Frederic Weisbecker <frederic@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Joel Fernandes <joel@...lfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Brian Gerst <brgerst@...il.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Will Deacon <will@...nel.org>
Subject: Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working
On Wed, Aug 19, 2020 at 11:42 AM <peterz@...radead.org> wrote:
>
> On Wed, Aug 19, 2020 at 10:53:58AM -0700, Kyle Huey wrote:
> > rr, a userspace record and replay debugger[0], has a test suite that
> > attempts to exercise strange corners of the Linux API. One such
> > test[1] began failing after 2bbc68f8373c0631ebf137f376fbea00e8086be7.
> > I have not tried to understand what has changed in the kernel here but
> > since the commit message says "No functional change" I assume
> > something has gone wrong.
> >
> > The test expects to get a SIGTRAP when watchvar is written to in the
> > forked child, but instead the program just exits normally and we get a
> > status value corresponding to that (exit code 77 = wait status
> > 0x4d00). This test program should be usable outside of rr's test suite
> > if you replace the test_assert/atomic_puts functions with
> > assert/printf and replace the util.h include with appropriate standard
> > includes.
> >
> > This regression is present in 5.8.
>
> $ uname -a
> Linux ivb-ep 5.9.0-rc1-dirty #343 SMP PREEMPT Wed Aug 19 15:04:35 CEST 2020 x86_64 GNU/Linux
>
> $ ./ptrace_debug_regs
> FAILED: errno=0 (Success)
> ptrace_debug_regs: ptrace_debug_regs.c:104: main: Assertion `"FAILED: !" && check_cond(status == ((5 << 8) | 0x7f))' failed.
> Aborted
>
> I'm guess that is not the expected outcome, is that the same failure you
> saw?
Yes. Is status also 0x4d00 for you?
The program is expected to complete with no assertions firing.
- Kyle
> ---
> /* -*- Mode: C; tab-width: 8; c-basic-offset: 2; indent-tabs-mode: nil; -*- */
>
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/ptrace.h>
> #include <stdarg.h>
> #include <assert.h>
> #include <sys/wait.h>
> #include <errno.h>
> #include <string.h>
> #include <stddef.h>
> #include <sys/user.h>
>
> /**
> * Print the printf-like arguments to stdout as atomic-ly as we can
> * manage. Async-signal-safe. Does not flush stdio buffers (doing so
> * isn't signal safe).
> */
> __attribute__((format(printf, 1, 2))) inline static int atomic_printf(
> const char* fmt, ...) {
> va_list args;
> char buf[1024];
> int len;
>
> va_start(args, fmt);
> len = vsnprintf(buf, sizeof(buf) - 1, fmt, args);
> va_end(args);
> return write(STDOUT_FILENO, buf, len);
> }
>
> /**
> * Write |str| on its own line to stdout as atomic-ly as we can
> * manage. Async-signal-safe. Does not flush stdio buffers (doing so
> * isn't signal safe).
> */
> inline static int atomic_puts(const char* str) {
> return atomic_printf("%s\n", str);
> }
>
> inline static int check_cond(int cond) {
> if (!cond) {
> atomic_printf("FAILED: errno=%d (%s)\n", errno, strerror(errno));
> }
> return cond;
> }
>
> #define test_assert(cond) assert("FAILED: !" && check_cond(cond))
>
> #define NEW_VALUE 0xabcdef
>
> static void breakpoint(void) {}
>
> static char watch_var;
>
> int main(void) {
> pid_t child;
> int status;
> int pipe_fds[2];
>
> test_assert(0 == pipe(pipe_fds));
>
> if (0 == (child = fork())) {
> char ch;
> read(pipe_fds[0], &ch, 1);
> breakpoint();
> watch_var = 1;
> return 77;
> }
>
> test_assert(0 == ptrace(PTRACE_ATTACH, child, NULL, NULL));
> test_assert(child == waitpid(child, &status, 0));
> test_assert(status == ((SIGSTOP << 8) | 0x7f));
> test_assert(1 == write(pipe_fds[1], "x", 1));
>
> test_assert(0 == ptrace(PTRACE_POKEUSER, child,
> (void*)offsetof(struct user, u_debugreg[0]),
> (void*)breakpoint));
> /* Enable DR0 break-on-exec */
> test_assert(0 == ptrace(PTRACE_POKEUSER, child,
> (void*)offsetof(struct user, u_debugreg[7]),
> (void*)0x1));
>
> test_assert(0 == ptrace(PTRACE_CONT, child, NULL, NULL));
> test_assert(child == waitpid(child, &status, 0));
> test_assert(status == ((SIGTRAP << 8) | 0x7f));
> test_assert(0x1 == ptrace(PTRACE_PEEKUSER, child,
> (void*)offsetof(struct user, u_debugreg[6])));
>
> test_assert(0 == ptrace(PTRACE_POKEUSER, child,
> (void*)offsetof(struct user, u_debugreg[0]),
> &watch_var));
> /* Enable DR0 break-on-write */
> test_assert(0 == ptrace(PTRACE_POKEUSER, child,
> (void*)offsetof(struct user, u_debugreg[7]),
> (void*)0x10001));
>
> test_assert(0 == ptrace(PTRACE_CONT, child, NULL, NULL));
> test_assert(child == waitpid(child, &status, 0));
> test_assert(status == ((SIGTRAP << 8) | 0x7f));
> test_assert(0x1 == ptrace(PTRACE_PEEKUSER, child,
> (void*)offsetof(struct user, u_debugreg[6])));
>
> test_assert(0 == ptrace(PTRACE_DETACH, child, NULL, NULL));
>
> test_assert(child == waitpid(child, &status, 0));
> test_assert(WIFEXITED(status));
> test_assert(WEXITSTATUS(status) == 77);
>
> atomic_puts("EXIT-SUCCESS");
> return 0;
> }
Powered by blists - more mailing lists