[PATCH 3/5] gpu: nova-core: vbios: use checked accesses in `setup_falcon_data`

[Eliot Courtney <ecourtney@nvidia.com>]

Use checked arithmetic and accesses where the values are firmware
derived to prevent potential overflow.

Fixes: dc70c6ae2441 ("gpu: nova-core: vbios: Add support to look up PMU table in FWSEC")
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
---
 drivers/gpu/nova-core/vbios.rs | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index de856000de23..2b0dc1a9125d 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -936,17 +936,12 @@ fn setup_falcon_data(
 
         self.falcon_data_offset = Some(offset);
 
-        if pmu_in_first_fwsec {
-            self.pmu_lookup_table = Some(PmuLookupTable::new(
-                &self.base.dev,
-                &first_fwsec.base.data[offset..],
-            )?);
+        let pmu_lookup_data = if pmu_in_first_fwsec {
+            &first_fwsec.base.data[offset..]
         } else {
-            self.pmu_lookup_table = Some(PmuLookupTable::new(
-                &self.base.dev,
-                &self.base.data[offset..],
-            )?);
-        }
+            self.base.data.get(offset..).ok_or(EINVAL)?
+        };
+        self.pmu_lookup_table = Some(PmuLookupTable::new(&self.base.dev, pmu_lookup_data)?);
 
         match self
             .pmu_lookup_table
@@ -955,8 +950,9 @@ fn setup_falcon_data(
             .find_entry_by_type(FALCON_UCODE_ENTRY_APPID_FWSEC_PROD)
         {
             Ok(entry) => {
-                let mut ucode_offset = usize::from_safe_cast(entry.data);
-                ucode_offset -= pci_at_image.base.data.len();
+                let mut ucode_offset = usize::from_safe_cast(entry.data)
+                    .checked_sub(pci_at_image.base.data.len())
+                    .ok_or(EINVAL)?;
                 if ucode_offset < first_fwsec.base.data.len() {
                     dev_err!(self.base.dev, "Falcon Ucode offset not in second Fwsec.\n");
                     return Err(EINVAL);

-- 
2.53.0