linux-kernel - [PATCH 29/33] riscv: kernel command line option to opt out of user cfi

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Message-Id: <20241001-v5_user_cfi_series-v1-29-3ba65b6e550f@rivosinc.com>
Date: Tue, 01 Oct 2024 09:06:34 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
 Andrew Morton <akpm@...ux-foundation.org>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
 Christian Brauner <brauner@...nel.org>, 
 Peter Zijlstra <peterz@...radead.org>, Oleg Nesterov <oleg@...hat.com>, 
 Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>, 
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 linux-mm@...ck.org, linux-riscv@...ts.infradead.org, 
 devicetree@...r.kernel.org, linux-arch@...r.kernel.org, 
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 alistair.francis@....com, richard.henderson@...aro.org, jim.shu@...ive.com, 
 andybnac@...il.com, kito.cheng@...ive.com, charlie@...osinc.com, 
 atishp@...osinc.com, evan@...osinc.com, cleger@...osinc.com, 
 alexghiti@...osinc.com, samitolvanen@...gle.com, broonie@...nel.org, 
 rick.p.edgecombe@...el.com, Deepak Gupta <debug@...osinc.com>
Subject: [PATCH 29/33] riscv: kernel command line option to opt out of user
 cfi

This commit adds a kernel command line option using which user cfi can be
disabled.

Signed-off-by: Deepak Gupta <debug@...osinc.com>
---
 arch/riscv/kernel/usercfi.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index 40c32258b6ec..d92b49261b58 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -17,6 +17,8 @@
 #include <asm/csr.h>
 #include <asm/usercfi.h>

+bool disable_riscv_usercfi;
+
 #define SHSTK_ENTRY_SIZE sizeof(void *)

 bool is_shstk_enabled(struct task_struct *task)
@@ -393,6 +395,9 @@ int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
 	unsigned long size = 0, addr = 0;
 	bool enable_shstk = false;

+	if (disable_riscv_usercfi)
+		return 0;
+
 	if (!cpu_supports_shadow_stack())
 		return -EINVAL;

@@ -472,6 +477,9 @@ int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status)
 {
 	bool enable_indir_lp = false;

+	if (disable_riscv_usercfi)
+		return 0;
+
 	if (!cpu_supports_indirect_br_lp_instr())
 		return -EINVAL;

@@ -504,3 +512,15 @@ int arch_lock_indir_br_lp_status(struct task_struct *task,

 	return 0;
 }
+
+static int __init setup_global_riscv_enable(char *str)
+{
+	if (strcmp(str, "true") == 0)
+		disable_riscv_usercfi = true;
+
+	pr_info("Setting riscv usercfi to be %s\n", (disable_riscv_usercfi ? "disabled" : "enabled"));
+
+	return 1;
+}
+
+__setup("disable_riscv_usercfi=", setup_global_riscv_enable);

-- 
2.45.0