[PATCH AUTOSEL 4.14 8/9] ARM: ensure the signal page contains defined contents

[Sasha Levin]

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

[ Upstream commit 9c698bff66ab4914bb3d71da7dc6112519bde23e ]

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 at kernel.org>
Signed-off-by: Russell King <rmk+kernel at armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 arch/arm/kernel/signal.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 02e6b6dfffa7e..19e4ff507209b 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -667,18 +667,20 @@ 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;
 }
-- 
2.27.0