linux-kernel - Re: [PATCH v12 23/28] riscv: kernel command line option to opt out of user cfi

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Message-ID: <CAKC1njQR9yARvWffjznjpeZK5zLFpg0-qCUo25_8niH29YL6uA@mail.gmail.com>
Date: Thu, 20 Mar 2025 15:31:09 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Radim Krčmář <rkrcmar@...tanamicro.com>
Cc: 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>, 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, 
	linux-riscv <linux-riscv-bounces@...ts.infradead.org>
Subject: Re: [PATCH v12 23/28] riscv: kernel command line option to opt out of
 user cfi

On Thu, Mar 20, 2025 at 2:35 PM Radim Krčmář <rkrcmar@...tanamicro.com> wrote:
>
> 2025-03-14T14:39:42-07:00, Deepak Gupta <debug@...osinc.com>:
> > 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 | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> >
> > diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
> > index d31d89618763..813162ce4f15 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)
> > @@ -396,6 +398,9 @@ 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;
> >
> > @@ -475,6 +480,9 @@ 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;
> >
> > @@ -507,3 +515,16 @@ 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);
>
> I'd prefer two command line options instead.

One for zicfilp and one for zicfiss ?
>
> In any case, I think we still document params in kernel-parameters.txt.

Noted, will do that.