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Subject[patch 32/54] UML - Improve host PTRACE_SYSEMU check
-stable review patch.  If anyone has any objections, please let us know.
---------------------
From: Jeff Dike <jdike@addtoit.com>

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.

This fixes a hang on boot on FC6 hosts with a broken PTRACE_SYSEMU.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--
arch/um/os-Linux/start_up.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
--- linux-2.6.21.4.orig/arch/um/os-Linux/start_up.c
+++ linux-2.6.21.4/arch/um/os-Linux/start_up.c
@@ -144,9 +144,7 @@ static int stop_ptraced_child(int pid, v
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_par
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;
--
-
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