linux-kernel - Re: [PATCH 4/7] riscv: Simplify text patching loops

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: <8bff47cf-659e-4344-b235-72b17ed0f37a@sifive.com>
Date: Wed, 27 Mar 2024 10:11:26 -0500
From: Samuel Holland <samuel.holland@...ive.com>
To: Björn Töpel <bjorn@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] riscv: Simplify text patching loops

Hi Björn,

On 2024-02-19 7:03 AM, Björn Töpel wrote:
> Samuel Holland <samuel.holland@...ive.com> writes:
> 
>> This reduces the number of variables and makes the code easier to parse.
>>
>> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
>> ---
>>
>>  arch/riscv/kernel/patch.c | 21 +++++++++++----------
>>  1 file changed, 11 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
>> index bccd9ed04a05..7f030b46eae5 100644
>> --- a/arch/riscv/kernel/patch.c
>> +++ b/arch/riscv/kernel/patch.c
>> @@ -155,7 +155,6 @@ NOKPROBE_SYMBOL(__patch_insn_write);
>>  
>>  static int patch_insn_set(void *addr, u8 c, size_t len)
>>  {
>> -	size_t patched = 0;
>>  	size_t size;
>>  	int ret = 0;
>>  
>> @@ -163,11 +162,12 @@ static int patch_insn_set(void *addr, u8 c, size_t len)
>>  	 * __patch_insn_set() can only work on 2 pages at a time so call it in a
>>  	 * loop with len <= 2 * PAGE_SIZE.
>>  	 */
>> -	while (patched < len && !ret) {
>> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
>> -		ret = __patch_insn_set(addr + patched, c, size);
>> +	while (len && !ret) {
>> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
>> +		ret = __patch_insn_set(addr, c, size);
> 
> While you're at it, do:
>   ret = __patch_insn_set(addr, c, size);
>   if (ret)
>           return ret;
>   ...
> return 0;
> }
> 
> and simplify the while-loop predicate?

Yes, this looks better and reduces the code size as well. I'll make this change
in v2.

Regards,
Samuel

>>  
>> -		patched += size;
>> +		addr += size;
>> +		len -= size;
>>  	}
>>  
>>  	return ret;
>> @@ -190,7 +190,6 @@ NOKPROBE_SYMBOL(patch_text_set_nosync);
>>  
>>  int patch_insn_write(void *addr, const void *insn, size_t len)
>>  {
>> -	size_t patched = 0;
>>  	size_t size;
>>  	int ret = 0;
>>  
>> @@ -198,11 +197,13 @@ int patch_insn_write(void *addr, const void *insn, size_t len)
>>  	 * Copy the instructions to the destination address, two pages at a time
>>  	 * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
>>  	 */
>> -	while (patched < len && !ret) {
>> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
>> -		ret = __patch_insn_write(addr + patched, insn + patched, size);
>> +	while (len && !ret) {
>> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
>> +		ret = __patch_insn_write(addr, insn, size);
> 
> Same comment as above.
> 
> 
> Björn