linux-kernel - Re: [PATCH] mm/cma: change print format of pointer in pr_debug() With %p, the pointer will be hashed and print (____ptrval___

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Message-ID: <ZYv01tdp6/igAkJN@casper.infradead.org>
Date: Wed, 27 Dec 2023 09:56:38 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Xiaobing Luo <luoxiaobing0926@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/cma: change print format of pointer in pr_debug()
 With %p, the pointer will be hashed and print (____ptrval____) instead.

On Wed, Dec 27, 2023 at 06:18:25AM +0000, Xiaobing Luo wrote:
>  [    0.070467] cma: cma_alloc(cma (____ptrval____), count 256, align 8)
>  [    0.073003] cma: cma_alloc(): returned (____ptrval____)
> 
> Use 0x%px instead of %p to print the pointer. Then the print will be like:
> 
>  [    0.054963] cma: cma_alloc(cma 0xffffffde9ad42a60, count 256, align 8)
>  [    0.057385] cma: cma_alloc(): returned 0xfffffffe003b0000

Please explain why we should leak this information to userspace,
making it easy for an attacker?