summaryrefslogtreecommitdiff
path: root/virt
diff options
context:
space:
mode:
authorPaolo Bonzini <pbonzini@redhat.com>2016-02-10 17:50:23 +0100
committerSasha Levin <sasha.levin@oracle.com>2016-03-07 16:35:09 -0500
commit0ccb848f62b5c9077cdeb903e324ca635806f804 (patch)
treee3f067440d645cb95aa177af491bdb00588e8eb8 /virt
parentb29de09dab6c486a7cecdf4741632fa48d903428 (diff)
KVM: x86: fix missed hardware breakpoints
[ Upstream commit 172b2386ed16a9143d9a456aae5ec87275c61489 ] Sometimes when setting a breakpoint a process doesn't stop on it. This is because the debug registers are not loaded correctly on VCPU load. The following simple reproducer from Oleg Nesterov tries using debug registers in two threads. To see the bug, run a 2-VCPU guest with "taskset -c 0" and run "./bp 0 1" inside the guest. #include <unistd.h> #include <signal.h> #include <stdlib.h> #include <stdio.h> #include <sys/wait.h> #include <sys/ptrace.h> #include <sys/user.h> #include <asm/debugreg.h> #include <assert.h> #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER) unsigned long encode_dr7(int drnum, int enable, unsigned int type, unsigned int len) { unsigned long dr7; dr7 = ((len | type) & 0xf) << (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE); if (enable) dr7 |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE)); return dr7; } int write_dr(int pid, int dr, unsigned long val) { return ptrace(PTRACE_POKEUSER, pid, offsetof (struct user, u_debugreg[dr]), val); } void set_bp(pid_t pid, void *addr) { unsigned long dr7; assert(write_dr(pid, 0, (long)addr) == 0); dr7 = encode_dr7(0, 1, DR_RW_EXECUTE, DR_LEN_1); assert(write_dr(pid, 7, dr7) == 0); } void *get_rip(int pid) { return (void*)ptrace(PTRACE_PEEKUSER, pid, offsetof(struct user, regs.rip), 0); } void test(int nr) { void *bp_addr = &&label + nr, *bp_hit; int pid; printf("test bp %d\n", nr); assert(nr < 16); // see 16 asm nops below pid = fork(); if (!pid) { assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0); kill(getpid(), SIGSTOP); for (;;) { label: asm ( "nop; nop; nop; nop;" "nop; nop; nop; nop;" "nop; nop; nop; nop;" "nop; nop; nop; nop;" ); } } assert(pid == wait(NULL)); set_bp(pid, bp_addr); for (;;) { assert(ptrace(PTRACE_CONT, pid, 0, 0) == 0); assert(pid == wait(NULL)); bp_hit = get_rip(pid); if (bp_hit != bp_addr) fprintf(stderr, "ERR!! hit wrong bp %ld != %d\n", bp_hit - &&label, nr); } } int main(int argc, const char *argv[]) { while (--argc) { int nr = atoi(*++argv); if (!fork()) test(nr); } while (wait(NULL) > 0) ; return 0; } Cc: stable@vger.kernel.org Suggested-by: Nadav Amit <namit@cs.technion.ac.il> Reported-by: Andrey Wagin <avagin@gmail.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'virt')
0 files changed, 0 insertions, 0 deletions