linux-kernel - Re: [PATCH v24 25/28] riscv: create a config for shadow stack and landing pad instr support

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Message-ID: <b5feba48-7e7c-4ab9-a193-072f3980f525@infradead.org>
Date: Thu, 4 Dec 2025 14:17:27 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Deepak Gupta <debug@...osinc.com>, 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>,
 Jann Horn <jannh@...gle.com>, Conor Dooley <conor+dt@...nel.org>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Benno Lossin <lossin@...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, rust-for-linux@...r.kernel.org,
 Zong Li <zong.li@...ive.com>, Andreas Korb
 <andreas.korb@...ec.fraunhofer.de>,
 Valentin Haudiquet <valentin.haudiquet@...onical.com>
Subject: Re: [PATCH v24 25/28] riscv: create a config for shadow stack and
 landing pad instr support

On 12/4/25 12:04 PM, Deepak Gupta wrote:
> This patch creates a config for shadow stack support and landing pad instr
> support. Shadow stack support and landing instr support can be enabled by
> selecting `CONFIG_RISCV_USER_CFI`. Selecting `CONFIG_RISCV_USER_CFI` wires
> up path to enumerate CPU support and if cpu support exists, kernel will
> support cpu assisted user mode cfi.
> 
> If CONFIG_RISCV_USER_CFI is selected, select `ARCH_USES_HIGH_VMA_FLAGS`,
> `ARCH_HAS_USER_SHADOW_STACK` and DYNAMIC_SIGFRAME for riscv.
> 
> Reviewed-by: Zong Li <zong.li@...ive.com>
> Tested-by: Andreas Korb <andreas.korb@...ec.fraunhofer.de>
> Tested-by: Valentin Haudiquet <valentin.haudiquet@...onical.com>
> Signed-off-by: Deepak Gupta <debug@...osinc.com>
> ---
>  arch/riscv/Kconfig                  | 22 ++++++++++++++++++++++
>  arch/riscv/configs/hardening.config |  4 ++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 0c6038dc5dfd..f5574c6f66d8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -1146,6 +1146,28 @@ config RANDOMIZE_BASE
>  
>            If unsure, say N.
>  
> +config RISCV_USER_CFI
> +	def_bool y
> +	bool "riscv userspace control flow integrity"
> +	depends on 64BIT && \
> +		$(cc-option,-mabi=lp64 -march=rv64ima_zicfiss_zicfilp -fcf-protection=full)
> +	depends on RISCV_ALTERNATIVE
> +	select RISCV_SBI
> +	select ARCH_HAS_USER_SHADOW_STACK
> +	select ARCH_USES_HIGH_VMA_FLAGS
> +	select DYNAMIC_SIGFRAME
> +	help
> +	  Provides CPU assisted control flow integrity to userspace tasks.

	           CPU-assisted

> +	  Control flow integrity is provided by implementing shadow stack for
> +	  backward edge and indirect branch tracking for forward edge in program.
> +	  Shadow stack protection is a hardware feature that detects function
> +	  return address corruption. This helps mitigate ROP attacks.
> +	  Indirect branch tracking enforces that all indirect branches must land
> +	  on a landing pad instruction else CPU will fault. This mitigates against
> +	  JOP / COP attacks. Applications must be enabled to use it, and old user-
> +	  space does not get protection "for free".
> +	  default y.

	  Default is y if hardware supports it.
?

> +
>  endmenu # "Kernel features"

-- 
~Randy