linux-kernel - Re: [PATCH 2/2] arm64/mm: Document why linear map split failure upon vm_reset

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: <ddfd7c74-d115-4f23-9a42-817e40321911@os.amperecomputing.com>
Date: Wed, 12 Nov 2025 14:34:24 -0800
From: Yang Shi <yang@...amperecomputing.com>
To: Dev Jain <dev.jain@....com>, catalin.marinas@....com, will@...nel.org
Cc: ryan.roberts@....com, rppt@...nel.org, shijie@...amperecomputing.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64/mm: Document why linear map split failure upon
 vm_reset_perms is not problematic



On 11/11/25 10:27 PM, Dev Jain wrote:
> Consider the following code path:
>
> (1) vmalloc -> (2) set_vm_flush_reset_perms -> (3) set_memory_ro/set_memory_rox
> -> .... (4) use the mapping .... -> (5) vfree -> (6) vm_reset_perms
> -> (7) set_area_direct_map.
> Or, it may happen that we encounter failure at (3) and directly jump to (5).
>
> In both cases, (7) may fail due to linear map split failure. But, we care
> about its success *only* for the region which got successfully changed by
> (3). Such a region is guaranteed to be pte-mapped.
>
> The TLDR is that (7) will surely succeed for the regions we care about.
>
> Signed-off-by: Dev Jain <dev.jain@....com>

Thanks for documenting this. Looks good to me. Reviewed-by: Yang Shi 
<yang@...amperecomputing.com>

Yang

> ---
>   arch/arm64/mm/pageattr.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index b4ea86cd3a71..dc05f06a47f2 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -185,6 +185,15 @@ static int change_memory_common(unsigned long addr, int numpages,
>   	 */
>   	if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
>   			    pgprot_val(clear_mask) == PTE_RDONLY)) {
> +		/*
> +		 * Note: One may wonder what happens if the calls to
> +		 * set_area_direct_map() in vm_reset_perms() fail due ENOMEM on
> +		 * linear map split failure. Observe that we care about those
> +		 * calls to succeed *only* for the region whose permissions
> +		 * are not default. Such a region is guaranteed to be
> +		 * pte-mapped, because the below call can change those
> +		 * permissions to non-default only after splitting that region.
> +		 */
>   		for (i = 0; i < area->nr_pages; i++) {
>   			ret = __change_memory_common((u64)page_address(area->pages[i]),
>   					       PAGE_SIZE, set_mask, clear_mask);