Messages in this thread | | | Date | Thu, 26 Jan 2006 11:41:55 -0500 | From | Chuck Ebbert <> | Subject | Re: [PATCH] i386 - sys_clone from vsyscall |
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In-Reply-To: <401b11ae0601260712w7cfe88abm638dc7a459b3bb3a@mail.gmail.com>
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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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