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Date:   Mon, 9 Mar 2020 13:21:38 +0100
From:   Greg KH <greg@kroah.com>
To:     Phong Tran <tranmanphong@gmail.com>
Cc:     Mark Rutland <mark.rutland@arm.com>, catalin.marinas@arm.com,
        will@kernel.org, alexios.zavras@intel.com, tglx@linutronix.de,
        akpm@linux-foundation.org, steven.price@arm.com,
        steve.capper@arm.com, broonie@kernel.org, keescook@chromium.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        kernel-hardening@lists.openwall.com
Subject: Re: [PATCH] arm64: add check_wx_pages debugfs for CHECK_WX
Message-ID: <20200309122138.GA206943@kroah.com>
References: <20200307093926.27145-1-tranmanphong@gmail.com>
 <20200309121713.GA26309@lakrids.cambridge.arm.com>
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On Mon, Mar 09, 2020 at 12:17:14PM +0000, Mark Rutland wrote:
> On Sat, Mar 07, 2020 at 04:39:26PM +0700, Phong Tran wrote:
> > follow the suggestion from
> > https://github.com/KSPP/linux/issues/35
> 
> That says:
> 
> | This should be implemented for all architectures
> 
> ... so surely this should be in generic code, rahter than being
> arm64-specific?
> 
> Thanks,
> Mark.
> 
> > 
> > Signed-off-by: Phong Tran <tranmanphong@gmail.com>
> > ---
> >  arch/arm64/Kconfig.debug        |  3 ++-
> >  arch/arm64/include/asm/ptdump.h |  2 ++
> >  arch/arm64/mm/dump.c            |  1 +
> >  arch/arm64/mm/ptdump_debugfs.c  | 18 ++++++++++++++++++
> >  4 files changed, 23 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> > index 1c906d932d6b..be552fa351e2 100644
> > --- a/arch/arm64/Kconfig.debug
> > +++ b/arch/arm64/Kconfig.debug
> > @@ -48,7 +48,8 @@ config DEBUG_WX
> >  	  of other unfixed kernel bugs easier.
> >  
> >  	  There is no runtime or memory usage effect of this option
> > -	  once the kernel has booted up - it's a one time check.
> > +	  once the kernel has booted up - it's a one time check and
> > +	  can be checked by echo "1" to "check_wx_pages" debugfs in runtime.
> >  
> >  	  If in doubt, say "Y".
> >  
> > diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
> > index 38187f74e089..b80d6b4fc508 100644
> > --- a/arch/arm64/include/asm/ptdump.h
> > +++ b/arch/arm64/include/asm/ptdump.h
> > @@ -24,9 +24,11 @@ struct ptdump_info {
> >  void ptdump_walk(struct seq_file *s, struct ptdump_info *info);
> >  #ifdef CONFIG_PTDUMP_DEBUGFS
> >  void ptdump_debugfs_register(struct ptdump_info *info, const char *name);
> > +int ptdump_check_wx_init(void);
> >  #else
> >  static inline void ptdump_debugfs_register(struct ptdump_info *info,
> >  					   const char *name) { }
> > +static inline int ptdump_check_wx_init(void) { return 0; }
> >  #endif
> >  void ptdump_check_wx(void);
> >  #endif /* CONFIG_PTDUMP_CORE */
> > diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
> > index 860c00ec8bd3..60c99a047763 100644
> > --- a/arch/arm64/mm/dump.c
> > +++ b/arch/arm64/mm/dump.c
> > @@ -378,6 +378,7 @@ static int ptdump_init(void)
> >  #endif
> >  	ptdump_initialize();
> >  	ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
> > +	ptdump_check_wx_init();
> >  	return 0;
> >  }
> >  device_initcall(ptdump_init);
> > diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c
> > index 1f2eae3e988b..73cddc12c3c2 100644
> > --- a/arch/arm64/mm/ptdump_debugfs.c
> > +++ b/arch/arm64/mm/ptdump_debugfs.c
> > @@ -16,3 +16,21 @@ void ptdump_debugfs_register(struct ptdump_info *info, const char *name)
> >  {
> >  	debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
> >  }
> > +
> > +static int check_wx_debugfs_set(void *data, u64 val)
> > +{
> > +	if (val != 1ULL)
> > +		return -EINVAL;
> > +
> > +	ptdump_check_wx();
> > +
> > +	return 0;
> > +}
> > +
> > +DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
> > +
> > +int ptdump_check_wx_init(void)
> > +{
> > +	return debugfs_create_file("check_wx_pages", 0200, NULL,
> > +				   NULL, &check_wx_fops) ? 0 : -ENOMEM;

Do not check the return value of this function, especially as it is
returning a pointer, not an int!

Just call the function and move on, you should not do anything different
if it returns an error or not.

thanks,

greg k-h