linux-kernel - [PATCH] Ensure kernel AI key is not changed on fork

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Date:   Thu, 20 May 2021 11:18:54 -0400
From:   Derrick McKee <derrick.mckee@...il.com>
To:     derrick.mckee@...il.com
Cc:     Nathan.Burow@...mit.edu, Yianni Giannaris <yiannig@....edu>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Ensure kernel AI key is not changed on fork

The kernel uses the IA key for PAC signing, 
and this key should remain unchanged from the kernel point of view.
This patch ensures that the IA key remains constant on fork, 
if it has been previously set.
The software is provided on an as-is basis.

Signed-off-by: Derrick McKee <derrick.mckee@...il.com>
Signed-off-by: Yianni Giannaris <yiannig@....edu>
---
 arch/arm64/include/asm/pointer_auth.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index d50416be99be..9748413e72fd 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -69,10 +69,13 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 	ptrauth_keys_install_user(keys);
 }
 
-static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
+static __always_inline void
+ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
 {
-	if (system_supports_address_auth())
-		get_random_bytes(&keys->apia, sizeof(keys->apia));
+	if (keys->apia.lo == 0 && keys->apia.hi == 0) {
+		if (system_supports_address_auth())
+			get_random_bytes(&keys->apia, sizeof(keys->apia));
+	}
 }
 
 static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kernel *keys)
-- 
2.31.1