linux-kernel - Re: [PATCH 1/1] pgo: Fix allocate_node() handling of non-vmlinux nodes.

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Message-ID: <202106021037.09943A41@keescook>
Date:   Wed, 2 Jun 2021 10:41:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jarmo Tiitto <jarmo.tiitto@...il.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Bill Wendling <wcw@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        morbo@...gle.com
Subject: Re: [PATCH 1/1] pgo: Fix allocate_node() handling of non-vmlinux
 nodes.

On Wed, Jun 02, 2021 at 03:57:04AM +0300, Jarmo Tiitto wrote:
> Currently allocate_node() will reserve nodes even if *p
> doesn't point into __llvm_prf_data_start - __llvm_prf_data_end
> range.
> 
> Fix it by checking if p points into vmlinux range
> and otherwise return NULL.
> 
> Signed-off-by: Jarmo Tiitto <jarmo.tiitto@...il.com>
> ---
>  kernel/pgo/instrument.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> index 0e07ee1b17d9..9bca535dfa91 100644
> --- a/kernel/pgo/instrument.c
> +++ b/kernel/pgo/instrument.c
> @@ -55,6 +55,10 @@ void prf_unlock(unsigned long flags)
>  static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
>  						 u32 index, u64 value)
>  {
> +	/* check if p points into vmlinux. If not, don't allocate. */
> +	if (p < __llvm_prf_data_start || p >= __llvm_prf_data_end)
> +		return NULL;

This should be a tighter check (struct llvm_prf_data has size, so just
checking for p < __llvm_prf_data_end isn't sufficient. I recommend using
the memory_contains() helper.

And I think this should be louder as it's entirely unexpected right
now. Perhaps:

	if (WARN_ON_ONCE(!memory_contains(__llvm_prf_data_start,
					  __llvm_prf_data_end,
					  p, sizeof(*p))))
		return NULL;

> +
>  	if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
>  		return NULL; /* Out of nodes */
>  
> -- 
> 2.31.1
> 

-- 
Kees Cook