linux-kernel - Re: [PATCH v7 07/11] arm64: unify native/compat instruction skipping

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Message-ID: <202002261341.17C9BC2222@keescook>
Date:   Wed, 26 Feb 2020 13:41:18 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Marc Zyngier <maz@...nel.org>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        "H . J . Lu " <hjl.tools@...il.com>,
        Andrew Jones <drjones@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Florian Weimer <fweimer@...hat.com>,
        Sudakshina Das <sudi.das@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Dave Martin <Dave.Martin@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v7 07/11] arm64: unify native/compat instruction skipping

On Wed, Feb 26, 2020 at 03:57:10PM +0000, Mark Brown wrote:
> From: Dave Martin <Dave.Martin@....com>
> 
> Skipping of an instruction on AArch32 works a bit differently from
> AArch64, mainly due to the different CPSR/PSTATE semantics.
> 
> Currently arm64_skip_faulting_instruction() is only suitable for
> AArch64, and arm64_compat_skip_faulting_instruction() handles the IT
> state machine but is local to traps.c.
> 
> Since manual instruction skipping implies a trap, it's a relatively
> slow path.
> 
> So, make arm64_skip_faulting_instruction() handle both compat and
> native, and get rid of the arm64_compat_skip_faulting_instruction()
> special case.
> 
> Signed-off-by: Dave Martin <Dave.Martin@....com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> Reviewed-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/kernel/traps.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index b8c714dda851..bc9f4292bfc3 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -272,6 +272,8 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
>  	}
>  }
>  
> +static void advance_itstate(struct pt_regs *regs);
> +
>  void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
>  {
>  	regs->pc += size;
> @@ -282,6 +284,9 @@ void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
>  	 */
>  	if (user_mode(regs))
>  		user_fastforward_single_step(current);
> +
> +	if (regs->pstate & PSR_MODE32_BIT)
> +		advance_itstate(regs);
>  }
>  
>  static LIST_HEAD(undef_hook);
> @@ -644,19 +649,12 @@ static void advance_itstate(struct pt_regs *regs)
>  	compat_set_it_state(regs, it);
>  }
>  
> -static void arm64_compat_skip_faulting_instruction(struct pt_regs *regs,
> -						   unsigned int sz)
> -{
> -	advance_itstate(regs);
> -	arm64_skip_faulting_instruction(regs, sz);
> -}
> -
>  static void compat_cntfrq_read_handler(unsigned int esr, struct pt_regs *regs)
>  {
>  	int reg = (esr & ESR_ELx_CP15_32_ISS_RT_MASK) >> ESR_ELx_CP15_32_ISS_RT_SHIFT;
>  
>  	pt_regs_write_reg(regs, reg, arch_timer_get_rate());
> -	arm64_compat_skip_faulting_instruction(regs, 4);
> +	arm64_skip_faulting_instruction(regs, 4);
>  }
>  
>  static const struct sys64_hook cp15_32_hooks[] = {
> @@ -676,7 +674,7 @@ static void compat_cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
>  
>  	pt_regs_write_reg(regs, rt, lower_32_bits(val));
>  	pt_regs_write_reg(regs, rt2, upper_32_bits(val));
> -	arm64_compat_skip_faulting_instruction(regs, 4);
> +	arm64_skip_faulting_instruction(regs, 4);
>  }
>  
>  static const struct sys64_hook cp15_64_hooks[] = {
> @@ -697,7 +695,7 @@ void do_cp15instr(unsigned int esr, struct pt_regs *regs)
>  		 * There is no T16 variant of a CP access, so we
>  		 * always advance PC by 4 bytes.
>  		 */
> -		arm64_compat_skip_faulting_instruction(regs, 4);
> +		arm64_skip_faulting_instruction(regs, 4);
>  		return;
>  	}
>  
> -- 
> 2.20.1
> 

-- 
Kees Cook