linux-kernel - [PATCH 3/3] arm64: Enable control of pointer authentication using early param

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Date:   Fri,  8 Jan 2021 16:29:23 -0800
From:   Srinivas Ramana <sramana@...eaurora.org>
To:     catalin.marinas@....com, will@...nel.org, pajay@....qualcomm.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Srinivas Ramana <sramana@...eaurora.org>,
        Prasad Sodagudi <psodagud@...eaurora.org>
Subject: [PATCH 3/3] arm64: Enable control of pointer authentication using early param

Add support to control turning off the pointer authentication
using a kernel command line early param.
This will help control pointer authentication feature for both kernel
and userspace without kernel changes.

Signed-off-by: Ajay Patil <pajay@....qualcomm.com>
Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
Signed-off-by: Srinivas Ramana <sramana@...eaurora.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++
 arch/arm64/kernel/cpufeature.c                  | 38 +++++++++++++++++++------
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c722ec19cd00..d6855e0a9085 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -373,6 +373,12 @@
 	arcrimi=	[HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 			Format: <io>,<irq>,<nodeID>
 
+	arm64.disable_ptr_auth=
+			[ARM64] Force disable Linux support for address
+			authentication (both user and in-kernel).
+			0 - Pointer authentication is enabled[Default]
+			1 - Pointer authentication is force disabled
+
 	ataflop=	[HW,M68k]
 
 	atarimouse=	[HW,MOUSE] Atari Mouse
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index b2ffa9eaaaff..bdaaff78240b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -164,6 +164,24 @@ static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap);
 
 static bool __system_matches_cap(unsigned int n);
 
+#ifdef CONFIG_ARM64_PTR_AUTH
+bool arm64_disable_ptr_auth;
+
+static int __init arm64_disable_ptr_auth_fn(char *buf)
+{
+	return strtobool(buf, &arm64_disable_ptr_auth);
+}
+early_param("arm64.disable_ptr_auth", arm64_disable_ptr_auth_fn);
+
+s64 ptr_auth_ftr_filter(const struct arm64_ftr_bits *ftrp, s64 val)
+{
+	if (arm64_disable_ptr_auth)
+		return 0;
+	else
+		return val;
+}
+#endif
+
 /*
  * NOTE: Any changes to the visibility of features should be kept in
  * sync with the documentation of the CPU feature register ABI.
@@ -193,17 +211,21 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = {
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_SPECRES_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_SB_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_FRINTTS_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
-		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_GPI_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
-		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_GPA_SHIFT, 4, 0),
+#ifdef CONFIG_ARM64_PTR_AUTH
+	FILTERED_ARM64_FTR_BITS(FTR_UNSIGNED, FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE,
+				ID_AA64ISAR1_GPI_SHIFT, 4, 0, ptr_auth_ftr_filter),
+	FILTERED_ARM64_FTR_BITS(FTR_UNSIGNED, FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE,
+				ID_AA64ISAR1_GPA_SHIFT, 4, 0, ptr_auth_ftr_filter),
+#endif
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_LRCPC_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_FCMA_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_JSCVT_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
-		       FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_API_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
-		       FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_APA_SHIFT, 4, 0),
+#ifdef CONFIG_ARM64_PTR_AUTH
+	FILTERED_ARM64_FTR_BITS(FTR_UNSIGNED, FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE,
+				ID_AA64ISAR1_API_SHIFT, 4, 0, ptr_auth_ftr_filter),
+	FILTERED_ARM64_FTR_BITS(FTR_UNSIGNED, FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE,
+				ID_AA64ISAR1_APA_SHIFT, 4, 0, ptr_auth_ftr_filter),
+#endif
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_DPB_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
-- 
2.7.4