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Commit cf6acedb authored by Jeff Dike's avatar Jeff Dike Committed by Linus Torvalds
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uml: improve PTRACE_SYSEMU checking 



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: default avatarJeff Dike <jdike@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent da90fa8f

arch/um/os-Linux/start_up.c

+16 −8
Original line number Original line Diff line number Diff line
@@ -144,9 +144,7 @@ static int stop_ptraced_child(int pid, void *stack, int exitcode, 
		int exit_with = WEXITSTATUS(status);

		int exit_with = WEXITSTATUS(status);

		if (exit_with == 2)

		if (exit_with == 2)

			non_fatal("check_ptrace : child exited with status 2. "

			non_fatal("check_ptrace : child exited with status 2. "

				  "Serious trouble happening! Try updating "

				  "\nDisabling SYSEMU support.\n");

				  "your host skas patch!\nDisabling SYSEMU "

				  "support.");

		non_fatal("check_ptrace : child exited with exitcode %d, while "

		non_fatal("check_ptrace : child exited with exitcode %d, while "

			  "expecting %d; status 0x%x\n", exit_with,

			  "expecting %d; status 0x%x\n", exit_with,

			  exitcode, status);

			  exitcode, status);
@@ -209,6 +207,7 @@ __uml_setup("nosysemu", nosysemu_cmd_param, 
static void __init check_sysemu(void)

static void __init check_sysemu(void)

{

{

	void *stack;

	void *stack;

	unsigned long regs[MAX_REG_NR];

	int pid, n, status, count=0;

	int pid, n, status, count=0;





	non_fatal("Checking syscall emulation patch for ptrace...");

	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",

		fatal("check_sysemu : expected SIGTRAP, got status = %d",

		      status);

		      status);





	n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET,

	if(ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)

		   os_getpid());

		fatal_perror("check_sysemu : PTRACE_GETREGS failed");

	if(n < 0)

	if(PT_SYSCALL_NR(regs) != __NR_getpid){

		fatal_perror("check_sysemu : failed to modify system call "

		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");

			  "return");

		goto fail;

	}





	if (stop_ptraced_child(pid, stack, 0, 0) < 0)

	if (stop_ptraced_child(pid, stack, 0, 0) < 0)

		goto fail_stopped;

		goto fail_stopped;