linux-kernel - Re: [PATCH] x86/its: Always return a writable page for dynamic thunks

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: <73aaf67c-3ece-4a9f-989d-a1d4aae6ab69@suse.com>
Date: Wed, 4 Jun 2025 13:54:57 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: x86@...nel.org
Cc: pawan.kumar.gupta@...ux.intel.com, peterz@...radead.org,
 linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com
Subject: Re: [PATCH] x86/its: Always return a writable page for dynamic thunks



On 6/4/25 13:47, Nikolay Borisov wrote:
> its_alloc unconditionally allocates and return a ROX page, but setting
> it RW is predicated on its_mod being set. This can cause a #GP on the
> memset in its_allocate_thunk() if its_mod is not set.
> 
> Since the function always returns a page, ensure it's always set
> writable so it can be initialized properly.
> 
> Fixes: 872df34d7c51 ("x86/its: Use dynamic thunks for indirect branches")
> Signed-off-by: Nikolay Borisov <nik.borisov@...e.com>
> ---
>   arch/x86/kernel/alternative.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index ecfe7b497cad..191e909636a5 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -199,6 +199,8 @@ static void *its_alloc(void)
>   	if (!page)
>   		return NULL;
>   
> +	execmem_make_temp_rw(page, PAGE_SIZE);

Actually this is not sufficient, in case we don't have its_mod set ergo 
its_fini_mod won't be executed I guess execmem_restore_rox should also 
be executed in its_allocate_thunk iff its_mod is not set?

> +
>   #ifdef CONFIG_MODULES
>   	if (its_mod) {
>   		void *tmp = krealloc(its_mod->its_page_array,
> @@ -210,7 +212,6 @@ static void *its_alloc(void)
>   		its_mod->its_page_array = tmp;
>   		its_mod->its_page_array[its_mod->its_num_pages++] = page;
>   
> -		execmem_make_temp_rw(page, PAGE_SIZE);
>   	}
>   #endif /* CONFIG_MODULES */
>