linux-kernel - Re: [PATCH] trace/events/page_ref: add page info to page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <8418b91e-04bb-4b74-96dd-a9489fbf9ba6@kernel.org>
Date: Thu, 31 Oct 2024 08:24:36 +0100
From: "Vlastimil Babka (SUSE)" <vbabka@...nel.org>
To: Kassey Li <quic_yingangl@...cinc.com>, akpm@...ux-foundation.org
Cc: minchan@...nel.org, vbabka@...e.cz, iamjoonsoo.kim@....com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] trace/events/page_ref: add page info to page_ref trace
 event

On 10/31/24 03:42, Kassey Li wrote:
> This followed
> commit 53d884a6675b ("mm, tracing: unify PFN format strings")
> to add page info.
> 
> In many kernel code we are talking with page other than pfn,
> here we added page algin with pfn.

How exactly would this help you, what are you doing with the trace?

> Signed-off-by: Kassey Li <quic_yingangl@...cinc.com>
> ---
>  include/trace/events/page_ref.h | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/page_ref.h b/include/trace/events/page_ref.h
> index fe33a255b7d0..76df13b2a5b3 100644
> --- a/include/trace/events/page_ref.h
> +++ b/include/trace/events/page_ref.h
> @@ -18,6 +18,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_template,
>  
>  	TP_STRUCT__entry(
>  		__field(unsigned long, pfn)
> +		__field(const struct page *, page)
>  		__field(unsigned long, flags)
>  		__field(int, count)
>  		__field(int, mapcount)
> @@ -28,6 +29,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_template,
>  
>  	TP_fast_assign(
>  		__entry->pfn = page_to_pfn(page);

pfn is derived from the page, but not subject to KASLR, so in that sense is
better.
If you need to correlate the trace with some other data you obtained that
does contains page pointers, you will have to postprocess the trace with a
pfn_to_page() step, which is rather simple (but you'll need to obtain and
supply the randomized base) or have that other data source give you pfn too.

The tracepoints should not reveal the randomized base as trivially as they
would do after this patch.

> +		__entry->page = page;
>  		__entry->flags = page->flags;
>  		__entry->count = page_ref_count(page);
>  		__entry->mapcount = atomic_read(&page->_mapcount);
> @@ -36,8 +38,9 @@ DECLARE_EVENT_CLASS(page_ref_mod_template,
>  		__entry->val = v;
>  	),
>  
> -	TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d",
> +	TP_printk("pfn=0x%lx page=%p flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d",
>  		__entry->pfn,
> +		__entry->page,
>  		show_page_flags(__entry->flags & PAGEFLAGS_MASK),
>  		__entry->count,
>  		__entry->mapcount, __entry->mapping, __entry->mt,
> @@ -66,6 +69,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,
>  
>  	TP_STRUCT__entry(
>  		__field(unsigned long, pfn)
> +		__field(const struct page *, page)
>  		__field(unsigned long, flags)
>  		__field(int, count)
>  		__field(int, mapcount)
> @@ -77,6 +81,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,
>  
>  	TP_fast_assign(
>  		__entry->pfn = page_to_pfn(page);
> +		__entry->page = page;
>  		__entry->flags = page->flags;
>  		__entry->count = page_ref_count(page);
>  		__entry->mapcount = atomic_read(&page->_mapcount);
> @@ -86,8 +91,9 @@ DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,
>  		__entry->ret = ret;
>  	),
>  
> -	TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d ret=%d",
> +	TP_printk("pfn=0x%lx page=%p flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d ret=%d",
>  		__entry->pfn,
> +		__entry->page,
>  		show_page_flags(__entry->flags & PAGEFLAGS_MASK),
>  		__entry->count,
>  		__entry->mapcount, __entry->mapping, __entry->mt,