[PATCH 5.4 22/60] ARM: ensure the signal page contains defined contents

Greg Kroah-Hartman
2021-02-15T15:40:12Z

From: Russell King <rmk+kernel@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@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@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 ab2568996ddb0..c01f76cd02422 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -694,18 +694,20 @@ 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