Messages in this thread | | | Date | Wed, 19 Aug 2020 23:35:34 +0200 | From | Peter Zijlstra <> | Subject | Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working |
| |
On Wed, Aug 19, 2020 at 12:28:16PM -0700, Kyle Huey wrote:
> > I'm guess that is not the expected outcome, is that the same failure you > > saw? > > Yes. Is status also 0x4d00 for you?
Indeed.
> The program is expected to complete with no assertions firing.
When I comment out the break-on-exec test, the break-on-write test succeeds.
When I add a few printk()'s to our #DB handler (6) the program will magically work again.
I'm not much for ptrace(), but are we sure the test program is well behaved?
The below also always works..
--- /* -*- 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)); test_assert(0 == ptrace(PTRACE_POKEUSER, child, (void*)offsetof(struct user, u_debugreg[1]), &watch_var)); test_assert(0 == ptrace(PTRACE_POKEUSER, child, (void*)offsetof(struct user, u_debugreg[7]), (void*)0x100005));
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_CONT, child, NULL, NULL)); test_assert(child == waitpid(child, &status, 0)); test_assert(status == ((SIGTRAP << 8) | 0x7f)); test_assert(0x2 == 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; }
| |