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 <[email protected]> Signed-off-by: Russell King <[email protected]>
josf · Feb 5, 2021 · 9c698bf · 9c698bf
1 parent 538eea5
commit 9c698bf
Showing 1 changed file with 8 additions and 6 deletions.
diff --git 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;
 }