um: Fix ptrace GETREGS/SETREGS bugs

This fix two related bugs:
* PTRACE_GETREGS doesn't get the right orig_ax (syscall) value
* PTRACE_SETREGS can't set the orig_ax value (erased by initial value)

Get rid of the now useless and error-prone get_syscall().

Fix inconsistent behavior in the ptrace implementation for i386 when
updating orig_eax automatically update the syscall number as well. This
is now updated in handle_syscall().

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Thomas Meyer <thomas@m3y3r.de>
Cc: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Cc: Anton Ivanov <aivanov@brocade.com>
Cc: Meredydd Luff <meredydd@senatehouse.org>
Cc: David Drysdale <drysdale@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Acked-by: Kees Cook <keescook@chromium.org>

1 files changed, 14 insertions, 12 deletions

diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index 1683b8efdfda..6cadce761bcf 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c
@@ -7,29 +7,31 @@
 #include <linux/ptrace.h>
 #include <kern_util.h>
 #include <sysdep/ptrace.h>
+#include <sysdep/ptrace_user.h>
 #include <sysdep/syscalls.h>
-#include <os.h>
 
 void handle_syscall(struct uml_pt_regs *r)
 {
         struct pt_regs *regs = container_of(r, struct pt_regs, regs);
-        long result;
         int syscall;
 
-        if (syscall_trace_enter(regs)) {
-                result = -ENOSYS;
+        /* Initialize the syscall number and default return value. */
+        UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
+        PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
+
+        if (syscall_trace_enter(regs))
                 goto out;
-        }
 
-        syscall = get_syscall(r);
+        /* Update the syscall number after orig_ax has potentially been updated
+         * with ptrace.
+         */
+        UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
+        syscall = UPT_SYSCALL_NR(r);
 
-        if ((syscall > __NR_syscall_max) || syscall < 0)
-                result = -ENOSYS;
-        else
-                result = EXECUTE_SYSCALL(syscall, regs);
+        if (syscall >= 0 && syscall <= __NR_syscall_max)
+                PT_REGS_SET_SYSCALL_RETURN(regs,
+                                EXECUTE_SYSCALL(syscall, regs));
 
 out:
-        PT_REGS_SET_SYSCALL_RETURN(regs, result);
-
         syscall_trace_leave(regs);
 }