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From: Ingo Molnar <mingo@kernel.org>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
	Changbin Du <changbin.du@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/mm: determine whether the fault address is canonical
Date: Mon, 7 Oct 2019 16:44:23 +0200	[thread overview]
Message-ID: <20191007144423.GA25181@gmail.com> (raw)
In-Reply-To: <20191007143255.GA59713@gmail.com>


* Ingo Molnar <mingo@kernel.org> wrote:

> > All the other reasons would require a fairly egregious kernel bug, hence
> > the speculation that the #GP is due to a non-canonical address.  Something
> > like the following would be more precise, though highly unlikely to ever
> > be exercised, e.g. KVM had a fatal bug related to injecting a non-zero
> > error code that went unnoticed for years.
> > 
> > 	WARN_ONCE(trapnr == X86_TRAP_GP, "General protection fault in user access. %s?\n",
> > 		  (IS_ENABLED(CONFIG_X86_64) && !error_code) ? "Non-canonical address" :
> > 		  					       "Segmentation bug");
> 
> Instead of trying to guess the reason of the #GPF (which guess might be 
> wrong), please just state it as the reason if we are sure that the cause 
> is a non-canonical address - and provide a best-guess if it's not but 
> clearly signal that it's a guess.
> 
> I.e. if I understood all the cases correctly we'd have three types of 
> messages generated:
> 
>  !error_code:
> 	"General protection fault in user access, due to non-canonical address."
> 
>  error_code && !is_canonical_addr(fault_addr):
> 	"General protection fault in user access. Non-canonical address?"
> 
>  error_code && is_canonical_addr(fault_addr):
> 	"General protection fault in user access. Segmentation bug?"

Now that I've read the rest of the thread, since fault_addr is always 0 
we can ignore most of this I suspect ...

Thanks,

	Ingo

  reply	other threads:[~2019-10-07 14:44 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-04 13:45 [PATCH] x86/mm: determine whether the fault address is canonical Changbin Du
2019-10-04 14:39 ` Dave Hansen
2019-10-04 15:31   ` Sean Christopherson
2019-10-07 14:32     ` Ingo Molnar
2019-10-07 14:44       ` Ingo Molnar [this message]
2019-10-07 15:13         ` Sean Christopherson
2019-10-04 14:59 ` Andy Lutomirski
2019-10-04 15:14   ` Dave Hansen
2019-10-06  2:29     ` Changbin Du

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