linux-kernel - Re: [PATCH 2/2] kprobes: Use struct_size() in __get_insn

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Message-Id: <20241031105855.6d88db454041f3cbd9723aab@kernel.org>
Date: Thu, 31 Oct 2024 10:58:55 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Naveen N Rao <naveen@...nel.org>, Anil S Keshavamurthy
 <anil.s.keshavamurthy@...el.com>, "David S. Miller" <davem@...emloft.net>,
 Kees Cook <kees@...nel.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Jinjie Ruan <ruanjinjie@...wei.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
 patches@...ts.linux.dev
Subject: Re: [PATCH 2/2] kprobes: Use struct_size() in __get_insn_slot()

On Wed, 30 Oct 2024 09:14:49 -0700
Nathan Chancellor <nathan@...nel.org> wrote:

> __get_insn_slot() allocates 'struct kprobe_insn_page' using a custom
> structure size calculation macro, KPROBE_INSN_PAGE_SIZE. Replace
> KPROBE_INSN_PAGE_SIZE with the struct_size() macro, which is the
> preferred way to calculate the size of flexible structures in the kernel
> because it handles overflow and makes it easier to change and audit how
> flexible structures are allocated across the entire tree.
> 

But I like this patch. I'll pick this.

Thank you!

> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  kernel/kprobes.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2cf4628bc97ce2ae18547b513cd75b6350e9cc9c..d452e784b31fa69042229ce0f5ffff9d8b671e92 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -95,10 +95,6 @@ struct kprobe_insn_page {
>  	char slot_used[] __counted_by(nused);
>  };
>  
> -#define KPROBE_INSN_PAGE_SIZE(slots)			\
> -	(offsetof(struct kprobe_insn_page, slot_used) +	\
> -	 (sizeof(char) * (slots)))
> -
>  static int slots_per_page(struct kprobe_insn_cache *c)
>  {
>  	return PAGE_SIZE/(c->insn_size * sizeof(kprobe_opcode_t));
> @@ -177,7 +173,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
>  		goto retry;
>  
>  	/* All out of space.  Need to allocate a new page. */
> -	kip = kmalloc(KPROBE_INSN_PAGE_SIZE(num_slots), GFP_KERNEL);
> +	kip = kmalloc(struct_size(kip, slot_used, num_slots), GFP_KERNEL);
>  	if (!kip)
>  		goto out;
>  
> 
> -- 
> 2.47.0
> 

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>