ARM: ensure the signal page contains defined contents

Ensure that the signal page contains our poison instruction to increase
the protection against ROP attacks and also contains well defined
contents.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 9d2e916121be4ebfc331b9771a553c66a6aa2e28..a3a38d0a4c853332102aefd01c02b0967e0ccc3f 100644 (file)
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -693,18 +693,20 @@ struct page *get_signal_page(void)
 
        addr = page_address(page);
 
+       /* Poison the entire page */
+       memset32(addr, __opcode_to_mem_arm(0xe7fddef1),
+                PAGE_SIZE / sizeof(u32));
+
        /* Give the signal return code some randomness */
        offset = 0x200 + (get_random_int() & 0x7fc);
        signal_return_offset = offset;
 
-       /*
-        * Copy signal return handlers into the vector page, and
-        * set sigreturn to be a pointer to these.
-        */
+       /* Copy signal return handlers into the page */
        memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
 
-       ptr = (unsigned long)addr + offset;
-       flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
+       /* Flush out all instructions in this page */
+       ptr = (unsigned long)addr;
+       flush_icache_range(ptr, ptr + PAGE_SIZE);
 
        return page;
 }