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authorAndy Lutomirski <luto@amacapital.net>2012-10-01 11:40:45 -0700
committerJames Morris <james.l.morris@oracle.com>2012-10-02 21:14:29 +1000
commit87b526d349b04c31d7b3a40b434eb3f825d22305 (patch)
tree2aeec0465901c9623ef7f5b3eb451ea6ccce6ecc /arch/x86
parentbf5308344527d015ac9a6d2bda4ad4d40fd7d943 (diff)
downloadop-kernel-dev-87b526d349b04c31d7b3a40b434eb3f825d22305.zip
op-kernel-dev-87b526d349b04c31d7b3a40b434eb3f825d22305.tar.gz
seccomp: Make syscall skipping and nr changes more consistent
This fixes two issues that could cause incompatibility between kernel versions: - If a tracer uses SECCOMP_RET_TRACE to select a syscall number higher than the largest known syscall, emulate the unknown vsyscall by returning -ENOSYS. (This is unlikely to make a noticeable difference on x86-64 due to the way the system call entry works.) - On x86-64 with vsyscall=emulate, skipped vsyscalls were buggy. This updates the documentation accordingly. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Acked-by: Will Drewry <wad@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kernel/vsyscall_64.c110
1 files changed, 59 insertions, 51 deletions
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 8d141b3..b2e58a2 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -136,19 +136,6 @@ static int addr_to_vsyscall_nr(unsigned long addr)
return nr;
}
-#ifdef CONFIG_SECCOMP
-static int vsyscall_seccomp(struct task_struct *tsk, int syscall_nr)
-{
- if (!seccomp_mode(&tsk->seccomp))
- return 0;
- task_pt_regs(tsk)->orig_ax = syscall_nr;
- task_pt_regs(tsk)->ax = syscall_nr;
- return __secure_computing(syscall_nr);
-}
-#else
-#define vsyscall_seccomp(_tsk, _nr) 0
-#endif
-
static bool write_ok_or_segv(unsigned long ptr, size_t size)
{
/*
@@ -181,10 +168,9 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
{
struct task_struct *tsk;
unsigned long caller;
- int vsyscall_nr;
+ int vsyscall_nr, syscall_nr, tmp;
int prev_sig_on_uaccess_error;
long ret;
- int skip;
/*
* No point in checking CS -- the only way to get here is a user mode
@@ -216,56 +202,84 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
}
tsk = current;
- /*
- * With a real vsyscall, page faults cause SIGSEGV. We want to
- * preserve that behavior to make writing exploits harder.
- */
- prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
- current_thread_info()->sig_on_uaccess_error = 1;
/*
+ * Check for access_ok violations and find the syscall nr.
+ *
* NULL is a valid user pointer (in the access_ok sense) on 32-bit and
* 64-bit, so we don't need to special-case it here. For all the
* vsyscalls, NULL means "don't write anything" not "write it at
* address 0".
*/
- ret = -EFAULT;
- skip = 0;
switch (vsyscall_nr) {
case 0:
- skip = vsyscall_seccomp(tsk, __NR_gettimeofday);
- if (skip)
- break;
-
if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
- !write_ok_or_segv(regs->si, sizeof(struct timezone)))
- break;
+ !write_ok_or_segv(regs->si, sizeof(struct timezone))) {
+ ret = -EFAULT;
+ goto check_fault;
+ }
+
+ syscall_nr = __NR_gettimeofday;
+ break;
+
+ case 1:
+ if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
+ ret = -EFAULT;
+ goto check_fault;
+ }
+
+ syscall_nr = __NR_time;
+ break;
+
+ case 2:
+ if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
+ !write_ok_or_segv(regs->si, sizeof(unsigned))) {
+ ret = -EFAULT;
+ goto check_fault;
+ }
+
+ syscall_nr = __NR_getcpu;
+ break;
+ }
+
+ /*
+ * Handle seccomp. regs->ip must be the original value.
+ * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
+ *
+ * We could optimize the seccomp disabled case, but performance
+ * here doesn't matter.
+ */
+ regs->orig_ax = syscall_nr;
+ regs->ax = -ENOSYS;
+ tmp = secure_computing(syscall_nr);
+ if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
+ warn_bad_vsyscall(KERN_DEBUG, regs,
+ "seccomp tried to change syscall nr or ip");
+ do_exit(SIGSYS);
+ }
+ if (tmp)
+ goto do_ret; /* skip requested */
+ /*
+ * With a real vsyscall, page faults cause SIGSEGV. We want to
+ * preserve that behavior to make writing exploits harder.
+ */
+ prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
+ current_thread_info()->sig_on_uaccess_error = 1;
+
+ ret = -EFAULT;
+ switch (vsyscall_nr) {
+ case 0:
ret = sys_gettimeofday(
(struct timeval __user *)regs->di,
(struct timezone __user *)regs->si);
break;
case 1:
- skip = vsyscall_seccomp(tsk, __NR_time);
- if (skip)
- break;
-
- if (!write_ok_or_segv(regs->di, sizeof(time_t)))
- break;
-
ret = sys_time((time_t __user *)regs->di);
break;
case 2:
- skip = vsyscall_seccomp(tsk, __NR_getcpu);
- if (skip)
- break;
-
- if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
- !write_ok_or_segv(regs->si, sizeof(unsigned)))
- break;
-
ret = sys_getcpu((unsigned __user *)regs->di,
(unsigned __user *)regs->si,
NULL);
@@ -274,12 +288,7 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
- if (skip) {
- if ((long)regs->ax <= 0L) /* seccomp errno emulation */
- goto do_ret;
- goto done; /* seccomp trace/trap */
- }
-
+check_fault:
if (ret == -EFAULT) {
/* Bad news -- userspace fed a bad pointer to a vsyscall. */
warn_bad_vsyscall(KERN_INFO, regs,
@@ -302,7 +311,6 @@ do_ret:
/* Emulate a ret instruction. */
regs->ip = caller;
regs->sp += 8;
-done:
return true;
sigsegv:
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