On 04/16, Oleg Nesterov wrote:
>
> On 04/16, Frederic Weisbecker wrote:
> >
> > On Sun, Mar 10, 2013 at 07:41:06PM +0100, Jiri Olsa wrote:
> > > Adding RF EFLAGS bit to be restored on return from signal from
> > > the original register context before the signal was entered.
> > >
> > > This will prevent the RF flag to disappear when returning
> > > from exception due to the signal handler being executed.
> >
> > So that happens if, say, we get a breakpoint exception and then we
> > run a signal handler before returning to the ip that triggered the
> > breakpoint?
>
> Afaics these changes (1 and 2) should fix the bug.
>
> Suppose that the first insn in the signal handler should trigger
> another bp, we should clear X86_EFLAGS_RF (2/6).
>
> Otoh, we should restore it when we return to the original insn
> which triggered the trap to avoid another trap.
I applied 1 and 2, and this fixes the test-case below.
> But. it seems that we have yet another problem? Suppose that
> the signal handler does siglongjmp() and jumps to yet another
> insn which should trigger the trap?
Argh. Sorry for confusion. I tried to say that the signal handler
can play with sigcontext->ip before sigreturn(). But probably we
can ignore this.
Oleg.
-------------------------------------------------------------------------------
#define _GNU_SOURCE 1
#include <stdio.h>
#include <unistd.h>
#include <sys/ptrace.h>
#include <sys/debugreg.h>
#include <sys/user.h>
#include <sys/wait.h>
#include <assert.h>
#include <assert.h>
#include <stddef.h>
#define DR_GLOBAL_ENABLE 0x2
#define DR_LOCAL_ENABLE 0x1
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);
}
#define GET_REG(pid, reg) \
ptrace(PTRACE_PEEKUSER, (pid), \
offsetof(struct user, regs.reg), 0)
void *get_ip(int pid)
{
return (void*)GET_REG(pid, rip);
}
void func(void)
{
printf("bp_1 passed\n");
}
void sigh(int sig)
{
printf("bp_2 passed\n");
}
int main(void)
{
int pid, stat;
unsigned long dr7;
pid = fork();
if (!pid) {
assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0);
kill(getpid(), SIGHUP);
signal(SIGINT, sigh);
func();
return 0x13;
}
assert(pid == waitpid(-1, &stat, 0));
assert(WSTOPSIG(stat) == SIGHUP);
assert(write_dr(pid, 0, (long)func) == 0);
assert(write_dr(pid, 1, (long)sigh) == 0);
dr7 = 0;
dr7 |= encode_dr7(0, 1, DR_RW_EXECUTE, DR_LEN_1);
dr7 |= encode_dr7(1, 1, DR_RW_EXECUTE, DR_LEN_1);
assert(write_dr(pid, 7, dr7) == 0);
assert(ptrace(PTRACE_CONT, pid, 0,0) == 0);
assert(pid == waitpid(-1, &stat, 0));
assert(WSTOPSIG(stat) == SIGTRAP);
assert(get_ip(pid) == func);
kill(pid, SIGINT);
assert(ptrace(PTRACE_CONT, pid, 0,0) == 0);
assert(pid == waitpid(-1, &stat, 0));
assert(WSTOPSIG(stat) == SIGINT);
assert(ptrace(PTRACE_CONT, pid, 0,SIGINT) == 0);
assert(pid == waitpid(-1, &stat, 0));
assert(WSTOPSIG(stat) == SIGTRAP);
assert(get_ip(pid) == sigh);
assert(ptrace(PTRACE_CONT, pid, 0,0) == 0);
assert(pid == waitpid(-1, &stat, 0));
assert(stat == 0x1300);
return 0;
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
