In-Reply-To: <[email protected]>
On Thu, 26 Jan 2006 at 15:12:08 +0000, Daniel fernandez wrote:
> > Your patch almost works but it copies the stack into the parent's address space.
> > Using access_process_vm() fixes it. However, that still leaves unfixed the case
> > where vsyscall-int80 is used.
>
> I copy the stack into the parent's address space becuase in this case
> the memory is shared, but access_process_vm() is more elegant :).
My test program (below) doesn't use CLONE_VM. With your patch the stack
data showed up only in the parent process, probably due to copy-on-write,
and the child gets SIGSEGV trying to transfer control to address 0.
> About vsyscall-int80, I don't know how to test that case in my
> computer but I think a solution could be:
I patched arch/i386/kernel/cpu/common.c to add a boot option "nox86sep"
similar to "nofxsr" and sure enough the test program dies when booting
with that option:
$ ./test_clone2.ex
SIGSEGV accessing 0x00000000 from EIP 0x00000000
cloned; ret = 621
Your fix for this should work fine.
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#ifdef INT80
# define SYSCALL_STR "int $0x80\n\t"
#else
# define SYSCALL_STR "call 0xffffe400\n\t"
#endif
#define CLONE 120
#define FLAGS 0
unsigned long child_stack[4096] __attribute__((__aligned__(4096)));
unsigned long *child_stack_ptr = &child_stack[2047];
struct sigaction sa;
int ret;
static void handler(int nr, siginfo_t *si, void *vuc)
{
struct ucontext *uc = (struct ucontext *)vuc;
struct sigcontext *sc = (struct sigcontext *)&uc->uc_mcontext;
printf("SIGSEGV accessing 0x%08x from EIP 0x%08x\n",
(unsigned long)si->si_addr, sc->eip);
sa.sa_handler = SIG_DFL;
sa.sa_flags = 0;
sigaction(SIGSEGV, &sa, NULL);
}
int main(int argc, char * const argv[])
{
sa.sa_sigaction = handler;
sa.sa_flags = SA_SIGINFO;
sigaction(SIGSEGV, &sa, NULL);
asm volatile(
SYSCALL_STR
: "=a"(ret)
: "a"(CLONE), "b"(FLAGS), "c"(child_stack_ptr)
: "memory"
);
printf("cloned; ret = %d\n", ret);
_exit(0);
}
--
Chuck
Currently reading: _The Atrocity Archives_ by Charles Stross
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