Restore ability for programs to upgrade themselves (#20265)

* Make helper associated fn

* Add feature definition

* Add handling to preserve program-id write lock when upgradeable loader is present; restore bpf upgrade-self test

* Use single feature

sdk/program/src/message/legacy.rs

@@ -354,6 +354,9 @@ impl Message {
     }
 
     pub fn is_writable(&self, i: usize, demote_program_write_locks: bool) -> bool {
+        let demote_program_id = demote_program_write_locks
+            && self.is_key_called_as_program(i)
+            && !self.is_upgradeable_loader_present();
         (i < (self.header.num_required_signatures - self.header.num_readonly_signed_accounts)
             as usize
             || (i >= self.header.num_required_signatures as usize
@@ -363,7 +366,7 @@ impl Message {
                 let key = self.account_keys[i];
                 sysvar::is_sysvar_id(&key) || BUILTIN_PROGRAMS_KEYS.contains(&key)
             }
-            && !(demote_program_write_locks && self.is_key_called_as_program(i))
+            && !demote_program_id
     }
 
     pub fn is_signer(&self, i: usize) -> bool {
@@ -503,6 +506,13 @@ impl Message {
         }
         false
     }
+
+    /// Returns true if any account is the bpf upgradeable loader
+    pub fn is_upgradeable_loader_present(&self) -> bool {
+        self.account_keys
+            .iter()
+            .any(|&key| key == bpf_loader_upgradeable::id())
+    }
 }
 
 #[cfg(test)]

sdk/program/src/message/mapped.rs

@@ -1,5 +1,6 @@
 use {
     crate::{
+        bpf_loader_upgradeable,
         message::{legacy::BUILTIN_PROGRAMS_KEYS, v0},
         pubkey::Pubkey,
         sysvar,
@@ -99,8 +100,12 @@ impl MappedMessage {
     pub fn is_writable(&self, key_index: usize, demote_program_write_locks: bool) -> bool {
         if self.is_writable_index(key_index) {
             if let Some(key) = self.get_account_key(key_index) {
-                return !(sysvar::is_sysvar_id(key) || BUILTIN_PROGRAMS_KEYS.contains(key)
-                    || (demote_program_write_locks && self.is_key_called_as_program(key_index)));
+                let demote_program_id = demote_program_write_locks
+                    && self.is_key_called_as_program(key_index)
+                    && !self.is_upgradeable_loader_present();
+                return !(sysvar::is_sysvar_id(key)
+                    || BUILTIN_PROGRAMS_KEYS.contains(key)
+                    || demote_program_id);
             }
         }
         false
@@ -116,6 +121,12 @@ impl MappedMessage {
             false
         }
     }
+
+    /// Returns true if any account is the bpf upgradeable loader
+    pub fn is_upgradeable_loader_present(&self) -> bool {
+        self.account_keys_iter()
+            .any(|&key| key == bpf_loader_upgradeable::id())
+    }
 }
 
 #[cfg(test)]

sdk/program/src/message/sanitized.rs

@@ -308,6 +308,14 @@ impl SanitizedMessage {
                 .saturating_add(num_secp256k1_signatures),
         )
     }
+
+    /// Inspect all message keys for the bpf upgradeable loader
+    pub fn is_upgradeable_loader_present(&self) -> bool {
+        match self {
+            Self::Legacy(message) => message.is_upgradeable_loader_present(),
+            Self::V0(message) => message.is_upgradeable_loader_present(),
+        }
+    }
 }
 
 #[cfg(test)]

sdk/src/feature_set.rs

@@ -264,7 +264,7 @@ lazy_static! {
         (instructions_sysvar_owned_by_sysvar::id(), "fix owner for instructions sysvar"),
         (close_upgradeable_program_accounts::id(), "enable closing upgradeable program accounts"),
         (stake_program_advance_activating_credits_observed::id(), "Enable advancing credits observed for activation epoch #19309"),
-        (demote_program_write_locks::id(), "demote program write locks to readonly #19593"),
+        (demote_program_write_locks::id(), "demote program write locks to readonly, except when upgradeable loader present #19593 #20265"),
         (ed25519_program_enabled::id(), "enable builtin ed25519 signature verify program"),
         (allow_native_ids::id(), "allow native program ids in program derived addresses"),
         (check_seed_length::id(), "Check program address seed lengths"),