linux-kernel - Re: [PATCH v5 6/8] x86/module: perpare module loading for ROX allocations of text

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Message-ID: <20241015082905.GA1235948@thelio-3990X>
Date: Tue, 15 Oct 2024 01:29:05 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v5 6/8] x86/module: perpare module loading for ROX
 allocations of text

On Fri, Oct 11, 2024 at 03:58:04PM +0300, Mike Rapoport wrote:
> I overlooked how cfi_*_callers routines update addr.
> This patch should fix it:

Thanks, can confirm. My boot is working again and LKDTM's
CFI_FORWARD_PROTO test properly fails.

> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 3b3fa93af3b1..cf782f431110 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -1148,11 +1148,13 @@ static int cfi_disable_callers(s32 *start, s32 *end, struct module *mod)
>  
>  	for (s = start; s < end; s++) {
>  		void *addr = (void *)s + *s;
> -		void *wr_addr = module_writable_address(mod, addr);
> +		void *wr_addr;
>  		u32 hash;
>  
>  		addr -= fineibt_caller_size;
> -		hash = decode_caller_hash(addr);
> +		wr_addr = module_writable_address(mod, addr);
> +		hash = decode_caller_hash(wr_addr);
> +
>  		if (!hash) /* nocfi callers */
>  			continue;
>  
> @@ -1172,11 +1174,12 @@ static int cfi_enable_callers(s32 *start, s32 *end, struct module *mod)
>  
>  	for (s = start; s < end; s++) {
>  		void *addr = (void *)s + *s;
> -		void *wr_addr = module_writable_address(mod, addr);
> +		void *wr_addr;
>  		u32 hash;
>  
>  		addr -= fineibt_caller_size;
> -		hash = decode_caller_hash(addr);
> +		wr_addr = module_writable_address(mod, addr);
> +		hash = decode_caller_hash(wr_addr);
>  		if (!hash) /* nocfi callers */
>  			continue;
>  
> @@ -1249,11 +1252,12 @@ static int cfi_rand_callers(s32 *start, s32 *end, struct module *mod)
>  
>  	for (s = start; s < end; s++) {
>  		void *addr = (void *)s + *s;
> -		void *wr_addr = module_writable_address(mod, addr);
> +		void *wr_addr;
>  		u32 hash;
>  
>  		addr -= fineibt_caller_size;
> -		hash = decode_caller_hash(addr);
> +		wr_addr = module_writable_address(mod, addr);
> +		hash = decode_caller_hash(wr_addr);
>  		if (hash) {
>  			hash = -cfi_rehash(hash);
>  			text_poke_early(wr_addr + 2, &hash, 4);
> @@ -1269,14 +1273,15 @@ static int cfi_rewrite_callers(s32 *start, s32 *end, struct module *mod)
>  
>  	for (s = start; s < end; s++) {
>  		void *addr = (void *)s + *s;
> -		void *wr_addr = module_writable_address(mod, addr);
> +		void *wr_addr;
>  		u32 hash;
>  
>  		addr -= fineibt_caller_size;
> -		hash = decode_caller_hash(addr);
> +		wr_addr = module_writable_address(mod, addr);
> +		hash = decode_caller_hash(wr_addr);
>  		if (hash) {
>  			text_poke_early(wr_addr, fineibt_caller_start, fineibt_caller_size);
> -			WARN_ON(*(u32 *)(addr + fineibt_caller_hash) != 0x12345678);
> +			WARN_ON(*(u32 *)(wr_addr + fineibt_caller_hash) != 0x12345678);
>  			text_poke_early(wr_addr + fineibt_caller_hash, &hash, 4);
>  		}
>  		/* rely on apply_retpolines() */
>  
> > Cheers,
> > Nathan
> 
> -- 
> Sincerely yours,
> Mike.