linux-hardening - Re: [PATCH v5 8/8] lkdtm/powerpc: Fix code patching hijack test

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Date:   Thu, 5 Aug 2021 11:18:04 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Christopher M. Riedl" <cmr@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     keescook@...omium.org, peterz@...radead.org, x86@...nel.org,
        npiggin@...il.com, linux-hardening@...r.kernel.org,
        tglx@...utronix.de, dja@...ens.net
Subject: Re: [PATCH v5 8/8] lkdtm/powerpc: Fix code patching hijack test



Le 13/07/2021 à 07:31, Christopher M. Riedl a écrit :
> Code patching on powerpc with a STRICT_KERNEL_RWX uses a userspace
> address in a temporary mm on Radix now. Use __put_user() to avoid write
> failures due to KUAP when attempting a "hijack" on the patching address.
> __put_user() also works with the non-userspace, vmalloc-based patching
> address on non-Radix MMUs.

It is not really clean to use __put_user() on non user address, allthought it works by change.

I think it would be better to do something like

	if (is_kernel_addr(addr))
		copy_to_kernel_nofault(...);
	else
		copy_to_user_nofault(...);



> 
> Signed-off-by: Christopher M. Riedl <cmr@...ux.ibm.com>
> ---
>   drivers/misc/lkdtm/perms.c | 9 ---------
>   1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> index 41e87e5f9cc86..da6a34a0a49fb 100644
> --- a/drivers/misc/lkdtm/perms.c
> +++ b/drivers/misc/lkdtm/perms.c
> @@ -262,16 +262,7 @@ static inline u32 lkdtm_read_patch_site(void)
>   /* Returns True if the write succeeds */
>   static inline bool lkdtm_try_write(u32 data, u32 *addr)
>   {
> -#ifdef CONFIG_PPC
> -	__put_kernel_nofault(addr, &data, u32, err);
> -	return true;
> -
> -err:
> -	return false;
> -#endif
> -#ifdef CONFIG_X86_64
>   	return !__put_user(data, addr);
> -#endif
>   }
>   
>   static int lkdtm_patching_cpu(void *data)
>