LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andrew Morton <akpm@linux-foundation.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, aryabinin@virtuozzo.com,
	dvyukov@google.com, mingo@redhat.com, peterz@infradead.org
Subject: Re: [PATCH 2/3] kcov: prefault the kcov_area
Date: Tue, 8 May 2018 15:51:58 -0700	[thread overview]
Message-ID: <20180508155158.7e6a789d950bcaf957c8c3bf@linux-foundation.org> (raw)
In-Reply-To: <20180504135535.53744-3-mark.rutland@arm.com>

On Fri,  4 May 2018 14:55:34 +0100 Mark Rutland <mark.rutland@arm.com> wrote:

> On many architectures the vmalloc area is lazily faulted in upon first
> access. This is problematic for KCOV, as __sanitizer_cov_trace_pc
> accesses the (vmalloc'd) kcov_area, and fault handling code may be
> instrumented. If an access to kcov_area faults, this will result in
> mutual recursion through the fault handling code and
> __sanitizer_cov_trace_pc(), eventually leading to stack corruption
> and/or overflow.
> 
> We can avoid this by faulting in the kcov_area before
> __sanitizer_cov_trace_pc() is permitted to access it. Once it has been
> faulted in, it will remain present in the process page tables, and will
> not fault again.
> 
> ...
>
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -324,6 +324,17 @@ static int kcov_close(struct inode *inode, struct file *filep)
>  	return 0;
>  }
>  
> +static void kcov_fault_in_area(struct kcov *kcov)

It would be nice to have a comment here explaining why the function
exists.

umm, this?

--- a/kernel/kcov.c~kcov-prefault-the-kcov_area-fix-fix
+++ a/kernel/kcov.c
@@ -324,6 +324,10 @@ static int kcov_close(struct inode *inod
 	return 0;
 }
 
+/*
+ * fault in a lazily-faulted vmalloc area, to avoid recursion issues if the
+ * vmalloc fault handler itself is instrumented.
+ */
 static void kcov_fault_in_area(struct kcov *kcov)
 {
 	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);

> +{
> +	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
> +	unsigned long *area = kcov->area;
> +	unsigned long offset;
> +
> +	for (offset = 0; offset < kcov->size; offset += stride) {
> +		READ_ONCE(area[offset]);
> +	}
> +}

  parent reply	other threads:[~2018-05-08 22:52 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 13:55 [PATCH 0/3] kcov: fix unexpected faults Mark Rutland
2018-05-04 13:55 ` [PATCH 1/3] kcov: ensure irq code sees a valid area Mark Rutland
2018-05-04 14:56   ` Mark Rutland
2018-05-04 13:55 ` [PATCH 2/3] kcov: prefault the kcov_area Mark Rutland
2018-05-04 14:36   ` Andrey Ryabinin
2018-05-04 14:38     ` Mark Rutland
2018-05-04 14:42       ` Andrey Ryabinin
2018-05-08 22:51   ` Andrew Morton [this message]
2018-05-09  9:41     ` Mark Rutland
2018-05-04 13:55 ` [PATCH 3/3] sched/core / kcov: avoid kcov_area during task switch Mark Rutland
2018-05-04 14:32   ` Andrey Ryabinin
2018-05-04 14:36     ` Mark Rutland

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180508155158.7e6a789d950bcaf957c8c3bf@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=aryabinin@virtuozzo.com \
    --cc=dvyukov@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --subject='Re: [PATCH 2/3] kcov: prefault the kcov_area' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).