Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 19 Aug 2020 20:41:49 +0200 | From | peterz@infradea ... | Subject | Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working |
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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?
--- /* -*- 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; }
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