[PATCH v5 05/22] gpu: nova-core: vbios: use checked ops and accesses in `FwSecBiosImage::ucode`

[Eliot Courtney]

Use checked arithmetic and access for extracting the microcode since the
offsets are firmware derived.

Fixes: 47c4846e4319 ("gpu: nova-core: vbios: Add support for FWSEC ucode extraction")
Reviewed-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Eliot Courtney <ecourtney@xxxxxxxxxx>
---
 drivers/gpu/nova-core/vbios.rs | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index 2ff67273fdff..c62d918a3041 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -1110,16 +1110,18 @@ pub(crate) fn header(&self) -> Result<FalconUCodeDesc> {
 
     /// Get the ucode data as a byte slice
     pub(crate) fn ucode(&self, desc: &FalconUCodeDesc) -> Result<&[u8]> {
-        let falcon_ucode_offset = self.falcon_ucode_offset;
+        let size = usize::from_safe_cast(
+            desc.imem_load_size()
+                .checked_add(desc.dmem_load_size())
+                .ok_or(ERANGE)?,
+        );
 
         // The ucode data follows the descriptor.
-        let ucode_data_offset = falcon_ucode_offset + desc.size();
-        let size = usize::from_safe_cast(desc.imem_load_size() + desc.dmem_load_size());
-
-        // Get the data slice, checking bounds in a single operation.
         self.base
             .data
-            .get(ucode_data_offset..ucode_data_offset + size)
+            .get(self.falcon_ucode_offset..)
+            .and_then(|data| data.get(desc.size()..))
+            .and_then(|data| data.get(..size))
             .ok_or(ERANGE)
             .inspect_err(|_| {
                 dev_err!(

-- 
2.54.0