[PATCH] aarch64: Respect p_flags when protecting code with PROT_BTI

[Carlos O'Donell]

On 7/23/20 8:17 AM, Szabolcs Nagy wrote:
> The 07/17/2020 15:52, Szabolcs Nagy wrote:
>> The 07/15/2020 16:44, Szabolcs Nagy wrote:
>>> i'd like to commit the attached patch for 2.32
>>
>> ping.
>>
>> or can i commit such a patch as a bug fix?
> 
> Carlos, is there any particular reason this is not approved for 2.32?
 
No, I missed it in my review.

OK for 2.32.
 
>>> From af3c11a811cfcc2b72f07efa0696c2200e928e12 Mon Sep 17 00:00:00 2001
>>> From: Szabolcs Nagy <szabolcs.nagy@arm.com>
>>> Date: Mon, 13 Jul 2020 11:28:18 +0100
>>> Subject: [PATCH] aarch64: Respect p_flags when protecting code with PROT_BTI
>>>
>>> Use PROT_READ and PROT_WRITE according to the load segment p_flags
>>> when adding PROT_BTI.
>>>
>>> This is before processing relocations which may drop PROT_BTI in
>>> case of textrels.  Executable stacks are not protected via PROT_BTI
>>> either.  PROT_BTI is hardening in case memory corruption happened,
>>> it's value is reduced if there is writable and executable memory
>>> available so missing it on such memory is fine, but we should
>>> respect the p_flags and should not drop PROT_WRITE.
>>> ---
>>>  sysdeps/aarch64/dl-bti.c | 9 ++++++++-
>>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c
>>> index 965ddcc732..196e462520 100644
>>> --- a/sysdeps/aarch64/dl-bti.c
>>> +++ b/sysdeps/aarch64/dl-bti.c
>>> @@ -24,13 +24,20 @@ static int
>>>  enable_bti (struct link_map *map, const char *program)
>>>  {
>>>    const ElfW(Phdr) *phdr;
>>> -  unsigned prot = PROT_READ | PROT_EXEC | PROT_BTI;
>>> +  unsigned prot;

OK.

>>>  
>>>    for (phdr = map->l_phdr; phdr < &map->l_phdr[map->l_phnum]; ++phdr)
>>>      if (phdr->p_type == PT_LOAD && (phdr->p_flags & PF_X))
>>>        {
>>>  	void *start = (void *) (phdr->p_vaddr + map->l_addr);
>>>  	size_t len = phdr->p_memsz;
>>> +
>>> +	prot = PROT_EXEC | PROT_BTI;
>>> +	if (phdr->p_flags & PF_R)
>>> +	  prot |= PROT_READ;
>>> +	if (phdr->p_flags & PF_W)
>>> +	  prot |= PROT_WRITE;

OK.

>>> +
>>>  	if (__mprotect (start, len, prot) < 0)
>>>  	  {
>>>  	    if (program)
>>> -- 
>>> 2.17.1
>>>
>>
>>
>> -- 
> 


-- 
Cheers,
Carlos.