powerpc: Sanitize stack pointer in signal handling code

On powerpc64 machines running 32-bit userspace, we can get garbage bits in the
stack pointer passed into the kernel.  Most places handle this correctly, but
the signal handling code uses the passed value directly for allocating signal
stack frames.

This fixes the issue by introducing a get_clean_sp function that returns a
sanitized stack pointer.  For 32-bit tasks on a 64-bit kernel, the stack
pointer is masked correctly.  In all other cases, the stack pointer is simply
returned.

Additionally, we pass an 'is_32' parameter to get_sigframe now in order to
get the properly sanitized stack.  The callers are know to be 32 or 64-bit
statically.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index d3466490104a557de496a0c531430948384e6264..9eed29eee604713957dc9cd64c933c0262928eb6 100644 (file)
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -313,6 +313,25 @@ static inline void prefetchw(const void *x)
 #define HAVE_ARCH_PICK_MMAP_LAYOUT
 #endif
 
+#ifdef CONFIG_PPC64
+static inline unsigned long get_clean_sp(struct pt_regs *regs, int is_32)
+{
+       unsigned long sp;
+
+       if (is_32)
+               sp = regs->gpr[1] & 0x0ffffffffUL;
+       else
+               sp = regs->gpr[1];
+
+       return sp;
+}
+#else
+static inline unsigned long get_clean_sp(struct pt_regs *regs, int is_32)
+{
+       return regs->gpr[1];
+}
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_POWERPC_PROCESSOR_H */

diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index a54405ebd7b0c35236cafedb3edee13bcfb67fb3..00b5078da9a3f10f2e34ba160c72db098f67c612 100644 (file)
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -26,12 +26,12 @@ int show_unhandled_signals = 0;
  * Allocate space for the signal frame
  */
 void __user * get_sigframe(struct k_sigaction *ka, struct pt_regs *regs,
-                          size_t frame_size)
+                          size_t frame_size, int is_32)
 {
         unsigned long oldsp, newsp;
 
         /* Default to using normal stack */
-        oldsp = regs->gpr[1];
+        oldsp = get_clean_sp(regs, is_32);
 
        /* Check for alt stack */
        if ((ka->sa.sa_flags & SA_ONSTACK) &&

diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
index f1442d69d4ece864af55c1e7889d01145dfc046f..6c0ddfc0603e80fa29c5a4b3408fa393d90e8f62 100644 (file)
--- a/arch/powerpc/kernel/signal.h
+++ b/arch/powerpc/kernel/signal.h
@@ -15,7 +15,7 @@
 extern void do_signal(struct pt_regs *regs, unsigned long thread_info_flags);
 
 extern void __user * get_sigframe(struct k_sigaction *ka, struct pt_regs *regs,
-                                 size_t frame_size);
+                                 size_t frame_size, int is_32);
 extern void restore_sigmask(sigset_t *set);
 
 extern int handle_signal32(unsigned long sig, struct k_sigaction *ka,

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index b13abf305996353735f0b1ec841fd8998da2e793..d670429a1608fe32a37a0b645df09aff7b904107 100644 (file)
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -836,7 +836,7 @@ int handle_rt_signal32(unsigned long sig, struct k_sigaction *ka,
 
        /* Set up Signal Frame */
        /* Put a Real Time Context onto stack */
-       rt_sf = get_sigframe(ka, regs, sizeof(*rt_sf));
+       rt_sf = get_sigframe(ka, regs, sizeof(*rt_sf), 1);
        addr = rt_sf;
        if (unlikely(rt_sf == NULL))
                goto badframe;
@@ -1182,7 +1182,7 @@ int handle_signal32(unsigned long sig, struct k_sigaction *ka,
        unsigned long newsp = 0;
 
        /* Set up Signal Frame */
-       frame = get_sigframe(ka, regs, sizeof(*frame));
+       frame = get_sigframe(ka, regs, sizeof(*frame), 1);
        if (unlikely(frame == NULL))
                goto badframe;
        sc = (struct sigcontext __user *) &frame->sctx;

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index e132891d3cea00e947750aa53ec97288a6f4c839..2fe6fc64b614ef9d1b935a472487eaf161967fd9 100644 (file)
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -402,7 +402,7 @@ int handle_rt_signal64(int signr, struct k_sigaction *ka, siginfo_t *info,
        unsigned long newsp = 0;
        long err = 0;
 
-       frame = get_sigframe(ka, regs, sizeof(*frame));
+       frame = get_sigframe(ka, regs, sizeof(*frame), 0);
        if (unlikely(frame == NULL))
                goto badframe;