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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 05:17:00 -0700
commit73a0285856e71d25fe61044e8c293e01c3851ccc (patch)
tree7bb12bd0540b604a3a3fec420655b4b722b05dd7
parent148ae97d28d13d9e32fc2e52e7c4c972e799a62f (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 d68b410595c8..a0c63fc48457 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);