From: Russell King
stable inclusion
from linux-4.19.177
commit 80ef523d2cb719c3de66787e922a96b5099d2fbb
category: bugfix
issue: #I42HM6
CVE: CVE-2021-21781
--------------------------------
[ 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
Signed-off-by: Russell King
Signed-off-by: Sasha Levin
Signed-off-by: Yang Yingliang
Signed-off-by: Yu Changchun
---
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 b908382b6..1c01358b9 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -697,18 +697,20 @@ 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;
}
--
2.22.0
