[PATCH 4.4 12/26] ARM: ensure the signal page contains defined contents

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Russell King <rmk+kernel@armlinux.org.uk>

commit 9c698bff66ab4914bb3d71da7dc6112519bde23e upstream.

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>
Signed-off-by: Nobuhiro Iwamatsu (CIP) <nobuhiro1.iwamatsu@toshiba.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm/kernel/signal.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -625,18 +625,20 @@ 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;
 }