[linux-morello] Re: [PATCH v2 16/22] lib/user_ptr: Add user pointer permission helpers for PCuABI

On 11/03/2024 10:28, Amit Daniel Kachhap wrote:

+user_ptr_perms_t user_ptr_perms_from_prot(int prot, bool has_tag_access) +{

• user_ptr_perms_t perms = 0;
• if (!reserv_is_supported(current->mm))

• return perms;
  

• if (mapping_may_have_prot_flag(prot, PROT_READ)) {

• perms |= CHERI_PERM_LOAD;
  

• if (has_tag_access)
  

• 	perms |= CHERI_PERM_LOAD_CAP;
  

• }
• if (mapping_may_have_prot_flag(prot, PROT_WRITE)) {

• perms |= CHERI_PERM_STORE;
  

• if (has_tag_access)
  

• 	perms |= (CHERI_PERM_STORE_CAP | CHERI_PERM_STORE_LOCAL_CAP);
  

• }
• if (mapping_may_have_prot_flag(prot, PROT_EXEC))

• perms |= CHERI_PERM_EXECUTE;
  

• /* Fetch any extra architecture specific permissions */
• perms |= arch_user_ptr_perms_from_prot(PROT_MAX_EXTRACT(prot) ?

• 			       PROT_MAX_EXTRACT(prot) : prot, has_tag_access);
  

I got confused for a moment looking at arch_user_ptr_perms_from_prot(), I thought PROT_MAX() was not being taken into account. I think doing it this way is fine, but then we might as well do the same in this function: calculate a local prot value first and then directly test PROT_{READ,WRITE,EXEC} in it, without the mapping_may_have_prot_flag() helper. This way it will look more similar to the arch_ helper and there is less risk of confusion.

Kevin

• perms |= CHERI_PERMS_ROOTCAP;
• return perms;

+}