[opentitantool] Add support for Google TPM "ready signal"

Google security chips deviate from the TPM standard. Because the chips are not able to meet the requirements for response/processing time, they employ an additional "ready" signal, generated by the GSC to indicate when it has finished processing the most recent request, and is ready to receive a new request. This CL adds an optional flag `--gsc_ready` to `opentitantool {spi,i2c} tpm` and to `tpm2_test_server`. Omitting this flag will result in `opentitantool` use the standard TPM protocol, specifying the flag will make `opentitantool` wait for the Google-specific ready signal at each transaction. Signed-off-by: Jes B. Klinke <[email protected]> Change-Id: I1fa442095cb85c3073500f66fdb38c5547b038d9
lowRISC · Feb 14, 2024 · c540024 · c540024
1 parent fb2c10b
commit c540024
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Showing 5 changed files with 124 additions and 12 deletions.
diff --git a/sw/host/opentitanlib/src/tpm/driver.rs b/sw/host/opentitanlib/src/tpm/driver.rs
@@ -5,11 +5,13 @@
 use anyhow::{bail, ensure, Result};
 use clap::ValueEnum;
 use serde::{Deserialize, Serialize};
+use std::borrow::Borrow;
 use std::rc::Rc;
 use std::thread;
 use std::time::{Duration, Instant};
 use thiserror::Error;
 
+use crate::io::gpio;
 use crate::io::i2c;
 use crate::io::spi;
 use crate::tpm::access::TpmAccess;
@@ -187,16 +189,43 @@ pub trait Driver {
     }
 }
 
+type GpioPinAndMonitoring = (Rc<dyn gpio::GpioPin>, Rc<dyn gpio::GpioMonitoring>);
+
+fn wait_for_gsc_ready(gsc_ready_pin: &Option<GpioPinAndMonitoring>) -> Result<()> {
+    let Some((gsc_ready_pin, monitoring)) = gsc_ready_pin else {
+        return Ok(());
+    };
+    let start_time = Instant::now();
+    while !monitoring
+        .monitoring_read(&[gsc_ready_pin.borrow()], true)?
+        .events
+        .into_iter()
+        .any(|e| e.edge == gpio::Edge::Falling)
+    {
+        if Instant::now().duration_since(start_time) > TIMEOUT {
+            bail!(TpmError::Timeout)
+        }
+    }
+    Ok(())
+}
+
 /// Implementation of the low level interface via standard SPI protocol.
 pub struct SpiDriver {
     spi: Rc<dyn spi::Target>,
+    gsc_ready_pin: Option<(Rc<dyn gpio::GpioPin>, Rc<dyn gpio::GpioMonitoring>)>,
 }
 
 impl SpiDriver {
     pub fn new(
         spi: Rc<dyn spi::Target>,
+        gsc_ready_pin: Option<(Rc<dyn gpio::GpioPin>, Rc<dyn gpio::GpioMonitoring>)>,
     ) -> Result<Self> {
-        Ok(Self { spi })
+        if let Some((gsc_ready_pin, monitoring)) = &gsc_ready_pin {
+            // Set up monitoring of edges on the GSC ready pin.  This will be more efficient than
+            // starting/stopping the monitoring on each TPM operation.
+            monitoring.monitoring_start(&[gsc_ready_pin.borrow()])?;
+        }
+        Ok(Self { spi, gsc_ready_pin })
     }
 
     /// Numerical TPM register address as used in SPI protocol.
@@ -295,6 +324,9 @@ impl Driver for SpiDriver {
             return Ok(());
         }
         let result = self.do_read_register(register, data);
+        if result.is_ok() {
+            wait_for_gsc_ready(&self.gsc_ready_pin)?;
+        }
         result
     }
 
@@ -315,20 +347,39 @@ impl Driver for SpiDriver {
             return Ok(());
         }
         let result = self.do_write_register(register, data);
+        if result.is_ok() {
+            wait_for_gsc_ready(&self.gsc_ready_pin)?;
+        }
         result
     }
 }
 
+impl Drop for SpiDriver {
+    fn drop(&mut self) {
+        if let Some((gsc_ready_pin, monitoring)) = &self.gsc_ready_pin {
+            // Stop monitoring of the gsc_ready pin, by reading one final time.
+            let _ = monitoring.monitoring_read(&[gsc_ready_pin.borrow()], false);
+        }
+    }
+}
+
 /// Implementation of the low level interface via Google I2C protocol.
 pub struct I2cDriver {
     i2c: Rc<dyn i2c::Bus>,
+    gsc_ready_pin: Option<(Rc<dyn gpio::GpioPin>, Rc<dyn gpio::GpioMonitoring>)>,
 }
 
 impl I2cDriver {
     pub fn new(
         i2c: Rc<dyn i2c::Bus>,
+        gsc_ready_pin: Option<(Rc<dyn gpio::GpioPin>, Rc<dyn gpio::GpioMonitoring>)>,
     ) -> Result<Self> {
-        Ok(Self { i2c })
+        if let Some((gsc_ready_pin, monitoring)) = &gsc_ready_pin {
+            // Set up monitoring of edges on the GSC ready pin.  This will be more efficient than
+            // starting/stopping the monitoring on each TPM operation.
+            monitoring.monitoring_start(&[gsc_ready_pin.borrow()])?;
+        }
+        Ok(Self { i2c, gsc_ready_pin })
     }
 
     /// Numerical TPM register address as used in Google I2C protocol.
@@ -343,13 +394,28 @@ impl I2cDriver {
     }
 
     fn try_read_register(&self, register: Register, data: &mut [u8]) -> Result<()> {
-        self.i2c.run_transaction(
-            None, /* default addr */
-            &mut [
-                i2c::Transfer::Write(&[Self::addr(register).unwrap()]),
-                i2c::Transfer::Read(data),
-            ],
-        )
+        if self.gsc_ready_pin.is_some() {
+            // Do two I2C transfers in one call, for lowest latency.
+            self.i2c.run_transaction(
+                None, /* default addr */
+                &mut [
+                    i2c::Transfer::Write(&[Self::addr(register).unwrap()]),
+                    i2c::Transfer::Read(data),
+                ],
+            )
+        } else {
+            // Since we need to check for the GSC ready signal in between, we have to do one I2C
+            // transfer at a time, and tolerate the latency of multiple roundtrip.
+            self.i2c.run_transaction(
+                None, /* default addr */
+                &mut [i2c::Transfer::Write(&[Self::addr(register).unwrap()])],
+            )?;
+            wait_for_gsc_ready(&self.gsc_ready_pin)?;
+            self.i2c.run_transaction(
+                None, /* default addr */
+                &mut [i2c::Transfer::Read(data)],
+            )
+        }
     }
 }
 
@@ -393,6 +459,16 @@ impl Driver for I2cDriver {
             None, /* default addr */
             &mut [i2c::Transfer::Write(&buffer)],
         )?;
+        wait_for_gsc_ready(&self.gsc_ready_pin)?;
         Ok(())
     }
 }
+
+impl Drop for I2cDriver {
+    fn drop(&mut self) {
+        if let Some((gsc_ready_pin, monitoring)) = &self.gsc_ready_pin {
+            // Stop monitoring of the gsc_ready pin, by reading one final time.
+            let _ = monitoring.monitoring_read(&[gsc_ready_pin.borrow()], false);
+        }
+    }
+}
diff --git a/sw/host/opentitantool/src/command/i2c.rs b/sw/host/opentitantool/src/command/i2c.rs
@@ -261,6 +261,10 @@ impl CommandDispatch for I2cPrepareRead {
 pub struct I2cTpm {
     #[command(subcommand)]
     command: super::tpm::TpmSubCommand,
+
+    /// Pin used for signalling by Google security chips
+    #[arg(long)]
+    gsc_ready: Option<String>,
 }
 
 impl CommandDispatch for I2cTpm {
@@ -270,8 +274,13 @@ impl CommandDispatch for I2cTpm {
         transport: &TransportWrapper,
     ) -> Result<Option<Box<dyn Annotate>>> {
         let context = context.downcast_ref::<I2cCommand>().unwrap();
+        let ready_pin = match &self.gsc_ready {
+            Some(pin) => Some((transport.gpio_pin(pin)?, transport.gpio_monitoring()?)),
+            None => None,
+        };
         let tpm_driver = Box::new(tpm::I2cDriver::new(
             context.params.create(transport, "TPM")?,
+            ready_pin,
         )?);
         self.command.run(&tpm_driver, transport)
     }

diff --git a/sw/host/opentitantool/src/command/spi.rs b/sw/host/opentitantool/src/command/spi.rs
@@ -310,6 +310,10 @@ impl CommandDispatch for SpiProgram {
 pub struct SpiTpm {
     #[command(subcommand)]
     command: super::tpm::TpmSubCommand,
+
+    /// Pin used for signalling by Google security chips
+    #[arg(long)]
+    gsc_ready: Option<String>,
 }
 
 impl CommandDispatch for SpiTpm {
@@ -319,8 +323,13 @@ impl CommandDispatch for SpiTpm {
         transport: &TransportWrapper,
     ) -> Result<Option<Box<dyn Annotate>>> {
         let context = context.downcast_ref::<SpiCommand>().unwrap();
+        let ready_pin = match &self.gsc_ready {
+            Some(pin) => Some((transport.gpio_pin(pin)?, transport.gpio_monitoring()?)),
+            None => None,
+        };
         let tpm_driver: Box<dyn tpm::Driver> = Box::new(tpm::SpiDriver::new(
             context.params.create(transport, "TPM")?,
+            ready_pin,
         )?);
         self.command.run(&tpm_driver, transport)
     }

diff --git a/sw/host/tests/chip/spi_device_tpm_test/src/main.rs b/sw/host/tests/chip/spi_device_tpm_test/src/main.rs
@@ -39,7 +39,7 @@ fn tpm_read_test(opts: &Opts, transport: &TransportWrapper) -> Result<()> {
 
     /* Wait sync message. */
     let _ = UartConsole::wait_for(&*uart, r"SYNC: Begin TPM Test\r\n", opts.timeout)?;
-    let tpm = tpm::SpiDriver::new(spi);
+    let tpm = tpm::SpiDriver::new(spi, None)?;
     const SIZE: usize = 10;
 
     for _ in 0..10 {

diff --git a/sw/host/tpm2_test_server/src/main.rs b/sw/host/tpm2_test_server/src/main.rs
@@ -19,10 +19,18 @@ pub enum TpmBus {
     Spi {
         #[command(flatten)]
         params: SpiParams,
+
+        /// Pin used for signalling by Google security chips
+        #[arg(long)]
+        gsc_ready: Option<String>,
     },
     I2C {
         #[command(flatten)]
         params: I2cParams,
+
+        /// Pin used for signalling by Google security chips
+        #[arg(long)]
+        gsc_ready: Option<String>,
     },
 }
 
@@ -74,16 +82,26 @@ pub fn main() -> anyhow::Result<()> {
 
     let transport = backend::create(&options.backend_opts)?;
     let bus: Box<dyn Driver> = match options.bus {
-        TpmBus::Spi { params } => {
+        TpmBus::Spi { params, gsc_ready } => {
             let spi = params.create(&transport, "TPM")?;
+            let ready_pin = match &gsc_ready {
+                Some(pin) => Some((transport.gpio_pin(pin)?, transport.gpio_monitoring()?)),
+                None => None,
+            };
             Box::new(SpiDriver::new(
                 spi,
+                ready_pin,
             )?)
         }
-        TpmBus::I2C { params } => {
+        TpmBus::I2C { params, gsc_ready } => {
             let i2c = params.create(&transport, "TPM")?;
+            let ready_pin = match &gsc_ready {
+                Some(pin) => Some((transport.gpio_pin(pin)?, transport.gpio_monitoring()?)),
+                None => None,
+            };
             Box::new(I2cDriver::new(
                 i2c,
+                ready_pin,
             )?)
         }
     };