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Subject[PATCH 2/3] vsyscall_64: allow SECCOMP_RET_TRACErs to skip
Date
Current quirky ptrace behavior with vsyscall and seccomp
does not allow tracers to bypass the call. This change
provides that ability by checking if orig_ax changed.

Signed-off-by: Will Drewry <wad@chromium.org>
---
arch/x86/kernel/vsyscall_64.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 5db36ca..5f9640c 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -142,11 +142,15 @@ static int addr_to_vsyscall_nr(unsigned long addr)
#ifdef CONFIG_SECCOMP
static int vsyscall_seccomp(struct task_struct *tsk, int syscall_nr)
{
+ int ret;
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);
+ ret = __secure_computing(syscall_nr);
+ if (task_pt_regs(tsk)->orig_ax != syscall_nr)
+ return 1; /* ptrace syscall skip */
+ return ret;
}
#else
#define vsyscall_seccomp(_tsk, _nr) 0
@@ -278,9 +282,9 @@ 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 */
+ if ((long)regs->ax <= 0L || skip == 1) /* seccomp errno/trace */
goto do_ret;
- goto done; /* seccomp trace/trap */
+ goto done; /* seccomp trap */
}

if (ret == -EFAULT) {
--
1.7.9.5


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