[linux-morello] Re: [PATCH 15/21] mm/cap_addr_mgmt: Add capability permission helpers for PCuABI

On 08/01/2024 11:23, Amit Daniel Kachhap wrote:

[...]

+cheri_perms_t mapping_to_capability_perm(int prot, bool has_tag_access) +{

• cheri_perms_t perms = 0;
• 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;
  

• if (cheri_perms_get(cheri_pcc_get()) & CHERI_PERM_SYSTEM_REGS)
  

cheri_pcc_get() gives you the current PCC, that is the kernel one. We don't have a generic way to access saved (user) capability registers at the moment (i.e. for PCC an equivalent of instruction_pointer()). Since we're already introducing an arch helper, we might as well add this permission there.

Kevin

• 	perms |= CHERI_PERM_SYSTEM_REGS;
  

• }
• /* Fetch any extra architecture specific permissions */
• perms |= arch_map_to_cap_perm(PROT_MAX_EXTRACT(prot) ? PROT_MAX_EXTRACT(prot) : prot,

• 		      has_tag_access);
  

• perms |= CHERI_PERMS_ROOTCAP;
• return perms;

} #endif /* CONFIG_CHERI_PURECAP_UABI */