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uml: improve PTRACE_SYSEMU checking

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Make the PTRACE_SYSEMU checking more robust.  It will make sure that system
call numbers are reported correctly.  If there is a problem, it will disable
PTRACE_SYSEMU use and use PTRACE_SYSCALL instead.

Thanks to Balaji G for helping reproduce this problem.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jeff Dike 2007-05-23 13:57:40 -07:00 committed by Linus Torvalds
parent da90fa8ff6
commit cf6acedbea
1 changed files with 16 additions and 8 deletions
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24
arch/um/os-Linux/start_up.c
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@ -144,9 +144,7 @@ static int stop_ptraced_child(int pid, void *stack, int exitcode,
int exit_with = WEXITSTATUS(status);
if (exit_with == 2)
non_fatal("check_ptrace : child exited with status 2. "
"Serious trouble happening! Try updating "
"your host skas patch!\nDisabling SYSEMU "
"support.");
"\nDisabling SYSEMU support.\n");
non_fatal("check_ptrace : child exited with exitcode %d, while "
"expecting %d; status 0x%x\n", exit_with,
exitcode, status);
@ -209,6 +207,7 @@ __uml_setup("nosysemu", nosysemu_cmd_param,
static void __init check_sysemu(void)
{
void *stack;
unsigned long regs[MAX_REG_NR];
int pid, n, status, count=0;
non_fatal("Checking syscall emulation patch for ptrace...");
@ -225,11 +224,20 @@ static void __init check_sysemu(void)
fatal("check_sysemu : expected SIGTRAP, got status = %d",
status);
n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET,
os_getpid());
if(n < 0)
fatal_perror("check_sysemu : failed to modify system call "
"return");
if(ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
fatal_perror("check_sysemu : PTRACE_GETREGS failed");
if(PT_SYSCALL_NR(regs) != __NR_getpid){
non_fatal("check_sysemu got system call number %d, "
"expected %d...", PT_SYSCALL_NR(regs), __NR_getpid);
goto fail;
}
n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET, os_getpid());
if(n < 0){
non_fatal("check_sysemu : failed to modify system call "
"return");
goto fail;
}
if (stop_ptraced_child(pid, stack, 0, 0) < 0)
goto fail_stopped;