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authorVineet Gupta <vgupta@synopsys.com>2015-03-26 11:14:41 +0530
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-05-13 05:15:43 -0700
commiteb7b2163c2c1bbac738be514e696d1b1a385c826 (patch)
tree07624973bde8479136fb3de858eed92a289f9886
parentad233850c2fa3057c0ba86e674ed9c26cc96ddd5 (diff)
ARC: signal handling robustify
commit e4140819dadc3624accac8294881bca8a3cba4ed upstream. A malicious signal handler / restorer can DOS the system by fudging the user regs saved on stack, causing weird things such as sigreturn returning to user mode PC but cpu state still being kernel mode.... Ensure that in sigreturn path status32 always has U bit; any other bogosity (gargbage PC etc) will be taken care of by normal user mode exceptions mechanisms. Reproducer signal handler: void handle_sig(int signo, siginfo_t *info, void *context) { ucontext_t *uc = context; struct user_regs_struct *regs = &(uc->uc_mcontext.regs); regs->scratch.status32 = 0; } Before the fix, kernel would go off to weeds like below: --------->8----------- [ARCLinux]$ ./signal-test Path: /signal-test CPU: 0 PID: 61 Comm: signal-test Not tainted 4.0.0-rc5+ #65 task: 8f177880 ti: 5ffe6000 task.ti: 8f15c000 [ECR ]: 0x00220200 => Invalid Write @ 0x00000010 by insn @ 0x00010698 [EFA ]: 0x00000010 [BLINK ]: 0x2007c1ee [ERET ]: 0x10698 [STAT32]: 0x00000000 : <-------- BTA: 0x00010680 SP: 0x5ffe7e48 FP: 0x00000000 LPS: 0x20003c6c LPE: 0x20003c70 LPC: 0x00000000 ... --------->8----------- Reported-by: Alexey Brodkin <abrodkin@synopsys.com> Signed-off-by: Vineet Gupta <vgupta@synopsys.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/arc/kernel/signal.c20
1 files changed, 16 insertions, 4 deletions
diff --git a/arch/arc/kernel/signal.c b/arch/arc/kernel/signal.c
index 7e95e1a86510..6763654239a2 100644
--- a/arch/arc/kernel/signal.c
+++ b/arch/arc/kernel/signal.c
@@ -131,6 +131,15 @@ SYSCALL_DEFINE0(rt_sigreturn)
/* Don't restart from sigreturn */
syscall_wont_restart(regs);
+ /*
+ * Ensure that sigreturn always returns to user mode (in case the
+ * regs saved on user stack got fudged between save and sigreturn)
+ * Otherwise it is easy to panic the kernel with a custom
+ * signal handler and/or restorer which clobberes the status32/ret
+ * to return to a bogus location in kernel mode.
+ */
+ regs->status32 |= STATUS_U_MASK;
+
return regs->r0;
badframe:
@@ -234,8 +243,11 @@ setup_rt_frame(int signo, struct k_sigaction *ka, siginfo_t *info,
/*
* handler returns using sigreturn stub provided already by userpsace
+ * If not, nuke the process right away
*/
- BUG_ON(!(ka->sa.sa_flags & SA_RESTORER));
+ if(!(ka->sa.sa_flags & SA_RESTORER))
+ return 1;
+
regs->blink = (unsigned long)ka->sa.sa_restorer;
/* User Stack for signal handler will be above the frame just carved */
@@ -302,12 +314,12 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
struct pt_regs *regs)
{
sigset_t *oldset = sigmask_to_save();
- int ret;
+ int failed;
/* Set up the stack frame */
- ret = setup_rt_frame(sig, ka, info, oldset, regs);
+ failed = setup_rt_frame(sig, ka, info, oldset, regs);
- if (ret)
+ if (failed)
force_sigsegv(sig, current);
else
signal_delivered(sig, info, ka, regs, 0);