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Date: Tue, 7 Aug 2018 16:18:46 +0200
From: Petr Mladek <pmladek@...e.com>
To: Joe Perches <joe@...ches.com>
Cc: Oleg Nesterov <oleg@...hat.com>, Palmer Dabbelt <palmer@...ive.com>,
	Albert Ou <aou@...s.berkeley.edu>, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH V2] riscv: Convert uses of REG_FMT to %p

On Sat 2018-07-28 09:39:57, Joe Perches wrote:
> Use %p pointer output instead of REG_FMT and cast the unsigned longs to
> (void *) to avoid exposing kernel addresses.
> 
> Miscellanea:
> 
> o Convert pr_cont to printk(KERN_DEFAULT as these uses are
>   new logging lines and not previous line continuations
> o Remove the now unused REG_FMT defines
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
> 
> v2: sigh: Add missing fault.c
> 
>  arch/riscv/include/asm/ptrace.h |  6 -----
>  arch/riscv/kernel/process.c     | 52 +++++++++++++++++++++--------------------
>  arch/riscv/kernel/traps.c       |  4 ++--
>  arch/riscv/mm/fault.c           |  6 ++---
>  4 files changed, 32 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
> index 2c5df945d43c..b123e723f8fa 100644
> --- a/arch/riscv/include/asm/ptrace.h
> +++ b/arch/riscv/include/asm/ptrace.h
> @@ -60,12 +60,6 @@ struct pt_regs {
>          unsigned long orig_a0;
>  };
>  
> -#ifdef CONFIG_64BIT
> -#define REG_FMT "%016lx"
> -#else
> -#define REG_FMT "%08lx"
> -#endif
> -
>  #define user_mode(regs) (((regs)->sstatus & SR_SPP) == 0)
>  
>  
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index d7c6ca7c95ae..7223f6715ff3 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -36,7 +36,7 @@
>  extern asmlinkage void ret_from_fork(void);
>  extern asmlinkage void ret_from_kernel_thread(void);
>  
> -void arch_cpu_idle(void)
> +void arch_yycpu_idle(void)
>  {
>  	wait_for_interrupt();
>  	local_irq_enable();
> @@ -46,31 +46,33 @@ void show_regs(struct pt_regs *regs)
>  {
>  	show_regs_print_info(KERN_DEFAULT);
>  
> -	pr_cont("sepc: " REG_FMT " ra : " REG_FMT " sp : " REG_FMT "\n",
> -		regs->sepc, regs->ra, regs->sp);
> -	pr_cont(" gp : " REG_FMT " tp : " REG_FMT " t0 : " REG_FMT "\n",
> -		regs->gp, regs->tp, regs->t0);
> -	pr_cont(" t1 : " REG_FMT " t2 : " REG_FMT " s0 : " REG_FMT "\n",
> -		regs->t1, regs->t2, regs->s0);
> -	pr_cont(" s1 : " REG_FMT " a0 : " REG_FMT " a1 : " REG_FMT "\n",
> -		regs->s1, regs->a0, regs->a1);
> -	pr_cont(" a2 : " REG_FMT " a3 : " REG_FMT " a4 : " REG_FMT "\n",
> -		regs->a2, regs->a3, regs->a4);
> -	pr_cont(" a5 : " REG_FMT " a6 : " REG_FMT " a7 : " REG_FMT "\n",
> -		regs->a5, regs->a6, regs->a7);
> -	pr_cont(" s2 : " REG_FMT " s3 : " REG_FMT " s4 : " REG_FMT "\n",
> -		regs->s2, regs->s3, regs->s4);
> -	pr_cont(" s5 : " REG_FMT " s6 : " REG_FMT " s7 : " REG_FMT "\n",
> -		regs->s5, regs->s6, regs->s7);
> -	pr_cont(" s8 : " REG_FMT " s9 : " REG_FMT " s10: " REG_FMT "\n",
> -		regs->s8, regs->s9, regs->s10);
> -	pr_cont(" s11: " REG_FMT " t3 : " REG_FMT " t4 : " REG_FMT "\n",
> -		regs->s11, regs->t3, regs->t4);
> -	pr_cont(" t5 : " REG_FMT " t6 : " REG_FMT "\n",
> -		regs->t5, regs->t6);
> +	printk(KERN_DEFAULT "sepc: %p ra : %p sp : %p\n",
> +	       (void *)regs->sepc, (void *)regs->ra, (void *)regs->sp);
> +	printk(KERN_DEFAULT " gp : %p tp : %p t0 : %p\n",
> +	       (void *)regs->gp, (void *)regs->tp, (void *)regs->t0);
> +	printk(KERN_DEFAULT " t1 : %p t2 : %p s0 : %p\n",
> +	       (void *)regs->t1, (void *)regs->t2, (void *)regs->s0);
> +	printk(KERN_DEFAULT " s1 : %p a0 : %p a1 : %p\n",
> +	       (void *)regs->s1, (void *)regs->a0, (void *)regs->a1);
> +	printk(KERN_DEFAULT " a2 : %p a3 : %p a4 : %p\n",
> +	       (void *)regs->a2, (void *)regs->a3, (void *)regs->a4);
> +	printk(KERN_DEFAULT " a5 : %p a6 : %p a7 : %p\n",
> +	       (void *)regs->a5, (void *)regs->a6, (void *)regs->a7);
> +	printk(KERN_DEFAULT " s2 : %p s3 : %p s4 : %p\n",
> +	       (void *)regs->s2, (void *)regs->s3, (void *)regs->s4);
> +	printk(KERN_DEFAULT " s5 : %p s6 : %p s7 : %p\n",
> +	       (void *)regs->s5, (void *)regs->s6, (void *)regs->s7);
> +	printk(KERN_DEFAULT " s8 : %p s9 : %p s10: %p\n",
> +	       (void *)regs->s8, (void *)regs->s9, (void *)regs->s10);
> +	printk(KERN_DEFAULT " s11: %p t3 : %p t4 : %p\n",
> +	       (void *)regs->s11, (void *)regs->t3, (void *)regs->t4);
> +	printk(KERN_DEFAULT " t5 : %p t6 : %p\n",
> +	       (void *)regs->t5, (void *)regs->t6);
>  
> -	pr_cont("sstatus: " REG_FMT " sbadaddr: " REG_FMT " scause: " REG_FMT "\n",
> -		regs->sstatus, regs->sbadaddr, regs->scause);
> +	printk(KERN_DEFAULT "sstatus: %p sbadaddr: %p scause: %p\n",
> +	       (void *)regs->sstatus,
> +	       (void *)regs->sbadaddr,
> +	       (void *)regs->scause);
>  }

This change makes the dump almost unusable. Note that registers contain any
kind of information, not only pointers.

My understanding is that %px was introduced because printing the
pointer directly is sometimes worth the security risk. IMHO, this
is one place where we want to risk printing the real value.

Anyway, it needs to be decided by security gurus. Adding some more
people into CC.


Best Regards,
Petr

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