core-bpf: special-case config program error codes

Author: buffalojoec

src/lib.rs

@@ -872,37 +872,79 @@ fn execute_instr(mut input: InstrContext) -> Option<InstrEffects> {
     let return_data = transaction_context.get_return_data().1.to_vec();
 
     Some(InstrEffects {
-        custom_err: if let Err(InstructionError::Custom(x)) = result {
-            Some(x)
+        custom_err: if let Err(InstructionError::Custom(code)) = result {
+            #[cfg(feature = "core-bpf")]
+            // See comment below under `result` for special-casing of custom
+            // errors for Core BPF programs.
+            if program_id == &solana_sdk::config::program::id() && (code == 0 || code == 1) {
+                None
+            } else {
+                Some(code)
+            }
+            #[cfg(not(feature = "core-bpf"))]
+            Some(code)
         } else {
             None
         },
         #[allow(clippy::map_identity)]
         result: result.err().map(|err| {
             #[cfg(feature = "core-bpf")]
-            // Some errors don't directly map between builtins and their BPF
-            // versions.
-            //
-            // For example, when a builtin program exceeds the compute budget,
-            // the builtin's `DEFAULT_COMPUTE_UNITS` are deducted from the
-            // meter, and if the meter is exhuasted, the invoke context will
-            // throw `InstructionError::ComputationalBudgetExceeded`.
-            // https://github.com/anza-xyz/agave/blob/6d74d13749829d463fabccebd8203edf0cf4c500/program-runtime/src/invoke_context.rs#L73
-            // https://github.com/anza-xyz/agave/blob/6d74d13749829d463fabccebd8203edf0cf4c500/program-runtime/src/invoke_context.rs#L574
-            //
-            // However, for a BPF program, if the compute meter is exhausted,
-            // the error comes from the VM, and is converted to
-            // `InstructionError::ProgramFailedToComplete`.
-            // https://github.com/solana-labs/rbpf/blob/69a52ec6a341bb7374d387173b5e6dc56218fe0c/src/error.rs#L44
-            // https://github.com/anza-xyz/agave/blob/6d74d13749829d463fabccebd8203edf0cf4c500/program-runtime/src/invoke_context.rs#L547
-            //
-            // Therefore, some errors require reconciliation when testing a BPF
-            // program against its builtin implementation.
-            if err == InstructionError::ProgramFailedToComplete
-                && (input.cu_avail <= CORE_BPF_DEFAULT_COMPUTE_UNITS
-                    || compute_units_consumed >= input.cu_avail)
             {
-                return InstructionError::ComputationalBudgetExceeded;
+                // Some errors don't directly map between builtins and their BPF
+                // versions.
+                //
+                // For example, when a builtin program exceeds the compute budget,
+                // the builtin's `DEFAULT_COMPUTE_UNITS` are deducted from the
+                // meter, and if the meter is exhuasted, the invoke context will
+                // throw `InstructionError::ComputationalBudgetExceeded`.
+                // https://github.com/anza-xyz/agave/blob/6d74d13749829d463fabccebd8203edf0cf4c500/program-runtime/src/invoke_context.rs#L73
+                // https://github.com/anza-xyz/agave/blob/6d74d13749829d463fabccebd8203edf0cf4c500/program-runtime/src/invoke_context.rs#L574
+                //
+                // However, for a BPF program, if the compute meter is exhausted,
+                // the error comes from the VM, and is converted to
+                // `InstructionError::ProgramFailedToComplete`.
+                // https://github.com/solana-labs/rbpf/blob/69a52ec6a341bb7374d387173b5e6dc56218fe0c/src/error.rs#L44
+                // https://github.com/anza-xyz/agave/blob/6d74d13749829d463fabccebd8203edf0cf4c500/program-runtime/src/invoke_context.rs#L547
+                //
+                // Therefore, some errors require reconciliation when testing a BPF
+                // program against its builtin implementation.
+                if err == InstructionError::ProgramFailedToComplete
+                    && (input.cu_avail <= CORE_BPF_DEFAULT_COMPUTE_UNITS
+                        || compute_units_consumed >= input.cu_avail)
+                {
+                    return InstructionError::ComputationalBudgetExceeded;
+                }
+                // Another such error case arises when a program performs a write
+                // to an account, but the data it writes is the exact same data
+                // that's currently stored in the account state.
+                //
+                // For builtins, the `TransactionContext` is invoked when any write
+                // is performed, asking it whether or not a write is allowed,
+                // regardless of the data being written. If the account is not
+                // writable, it throws `InstructionError::ReadonlyDataModified`.
+                //
+                // For BPF programs, writes to readonly accounts are caught _after_
+                // the VM finishes execution, when the loader inspects the
+                // serialized input data region. If a write was performed that did
+                // not modify serialized account state, then no error is thrown.
+                //
+                // As a result, Core BPF programs have been outfitted with custom
+                // errors when `is_writable` checks fail. These errors are
+                // special-cased below to avoid fixture mismatches.
+                match err {
+                    InstructionError::Custom(code) => {
+                        if program_id == &solana_sdk::config::program::id() {
+                            // Special-cased custom error codes for the Config program.
+                            if code == 0 {
+                                return InstructionError::ExecutableDataModified;
+                            }
+                            if code == 1 {
+                                return InstructionError::ReadonlyDataModified;
+                            }
+                        }
+                    }
+                    _ => {}
+                }
             }
             err
         }),