x86-64: Improve vsyscall emulation CS and RIP handling

Three fixes here:
 - Send SIGSEGV if called from compat code or with a funny CS.
 - Don't BUG on impossible addresses.
 - Add a missing local_irq_disable.

This patch also removes an unused variable.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Link: http://lkml.kernel.org/r/6fb2b13ab39b743d1e4f466eef13425854912f7f.1310563276.git.luto@mit.edu
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index bb710cb..d555973 100644 (file)
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -31,18 +31,6 @@ extern struct timezone sys_tz;
 
 extern void map_vsyscall(void);
 
-/* Emulation */
-
-static inline bool is_vsyscall_entry(unsigned long addr)
-{
-       return (addr & ~0xC00UL) == VSYSCALL_START;
-}
-
-static inline int vsyscall_entry_nr(unsigned long addr)
-{
-       return (addr & 0xC00UL) >> 10;
-}
-
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_X86_VSYSCALL_H */

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 10cd8ac..a262400 100644 (file)
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -38,6 +38,7 @@
 
 #include <asm/vsyscall.h>
 #include <asm/pgtable.h>
+#include <asm/compat.h>
 #include <asm/page.h>
 #include <asm/unistd.h>
 #include <asm/fixmap.h>
@@ -97,33 +98,63 @@ static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
 
        tsk = current;
 
-       printk("%s%s[%d] %s ip:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
+       printk("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
               level, tsk->comm, task_pid_nr(tsk),
-              message, regs->ip - 2, regs->sp, regs->ax, regs->si, regs->di);
+              message, regs->ip - 2, regs->cs,
+              regs->sp, regs->ax, regs->si, regs->di);
+}
+
+static int addr_to_vsyscall_nr(unsigned long addr)
+{
+       int nr;
+
+       if ((addr & ~0xC00UL) != VSYSCALL_START)
+               return -EINVAL;
+
+       nr = (addr & 0xC00UL) >> 10;
+       if (nr >= 3)
+               return -EINVAL;
+
+       return nr;
 }
 
 void dotraplinkage do_emulate_vsyscall(struct pt_regs *regs, long error_code)
 {
-       const char *vsyscall_name;
        struct task_struct *tsk;
        unsigned long caller;
        int vsyscall_nr;
        long ret;
 
-       /* Kernel code must never get here. */
-       BUG_ON(!user_mode(regs));
-
        local_irq_enable();
 
        /*
+        * Real 64-bit user mode code has cs == __USER_CS.  Anything else
+        * is bogus.
+        */
+       if (regs->cs != __USER_CS) {
+               /*
+                * If we trapped from kernel mode, we might as well OOPS now
+                * instead of returning to some random address and OOPSing
+                * then.
+                */
+               BUG_ON(!user_mode(regs));
+
+               /* Compat mode and non-compat 32-bit CS should both segfault. */
+               warn_bad_vsyscall(KERN_WARNING, regs,
+                                 "illegal int 0xcc from 32-bit mode");
+               goto sigsegv;
+       }
+
+       /*
         * x86-ism here: regs->ip points to the instruction after the int 0xcc,
         * and int 0xcc is two bytes long.
         */
-       if (!is_vsyscall_entry(regs->ip - 2)) {
-               warn_bad_vsyscall(KERN_WARNING, regs, "illegal int 0xcc (exploit attempt?)");
+       vsyscall_nr = addr_to_vsyscall_nr(regs->ip - 2);
+       if (vsyscall_nr < 0) {
+               warn_bad_vsyscall(KERN_WARNING, regs,
+                                 "illegal int 0xcc (exploit attempt?)");
                goto sigsegv;
        }
-       vsyscall_nr = vsyscall_entry_nr(regs->ip - 2);
 
        if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
                warn_bad_vsyscall(KERN_WARNING, regs, "int 0xcc with bad stack (exploit attempt?)");
@@ -136,31 +167,20 @@ void dotraplinkage do_emulate_vsyscall(struct pt_regs *regs, long error_code)
 
        switch (vsyscall_nr) {
        case 0:
-               vsyscall_name = "gettimeofday";
                ret = sys_gettimeofday(
                        (struct timeval __user *)regs->di,
                        (struct timezone __user *)regs->si);
                break;
 
        case 1:
-               vsyscall_name = "time";
                ret = sys_time((time_t __user *)regs->di);
                break;
 
        case 2:
-               vsyscall_name = "getcpu";
                ret = sys_getcpu((unsigned __user *)regs->di,
                                 (unsigned __user *)regs->si,
                                 0);
                break;
-
-       default:
-               /*
-                * If we get here, then vsyscall_nr indicates that int 0xcc
-                * happened at an address in the vsyscall page that doesn't
-                * contain int 0xcc.  That can't happen.
-                */
-               BUG();
        }
 
        if (ret == -EFAULT) {
@@ -188,6 +208,7 @@ void dotraplinkage do_emulate_vsyscall(struct pt_regs *regs, long error_code)
 sigsegv:
        regs->ip -= 2;  /* The faulting instruction should be the int 0xcc. */
        force_sig(SIGSEGV, current);
+       local_irq_disable();
 }
 
 /*