[PATCH] gpu: nova-core: parse structs via zerocopy

[Nicolás Antinori]

Replace the unsafe `kernel::transmute::FromBytes` trait implementation
for the `FalconUCodeDescV3`, `PcirStruct`, `BitHeader`, `NpdeStruct`,
and `PmuLookupTableHeader` structs with the derivable
`zerocopy::FromBytes` trait.

This change eliminates the manual unsafe implementations in favor of a
derivable trait. When this trait is derived, validity checks are
performed at compile time to make sure that the type can safely
implement `FromBytes`.

Link: https://github.com/Rust-for-Linux/linux/issues/1241
Suggested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Signed-off-by: Nicolás Antinori <nico.antinori.7@xxxxxxxxx>
---
NOTE: Compile-tested only. I don't own a piece of hardware where I can
test the nova driver.

 drivers/gpu/nova-core/firmware.rs |  6 +----
 drivers/gpu/nova-core/vbios.rs    | 38 ++++++++-----------------------
 2 files changed, 11 insertions(+), 33 deletions(-)

diff --git a/drivers/gpu/nova-core/firmware.rs b/drivers/gpu/nova-core/firmware.rs
index ad37994ac15a..0afd1d3fe5ad 100644
--- a/drivers/gpu/nova-core/firmware.rs
+++ b/drivers/gpu/nova-core/firmware.rs
@@ -86,7 +86,7 @@ pub(crate) struct FalconUCodeDescV2 {

 /// Structure used to describe some firmwares, notably FWSEC-FRTS.
 #[repr(C)]
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, FromBytes)]
 pub(crate) struct FalconUCodeDescV3 {
     /// Header defined by `NV_BIT_FALCON_UCODE_DESC_HEADER_VDESC*` in OpenRM.
     hdr: u32,
@@ -117,10 +117,6 @@ pub(crate) struct FalconUCodeDescV3 {
     _reserved: u16,
 }

-// SAFETY: all bit patterns are valid for this type, and it doesn't use
-// interior mutability.
-unsafe impl FromBytes for FalconUCodeDescV3 {}
-
 /// Enum wrapping the different versions of Falcon microcode descriptors.
 ///
 /// This allows handling both V2 and V3 descriptor formats through a
diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index 8b7d17a24660..754812bcbdde 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -13,11 +13,8 @@
         Alignment, //
     },
     sync::aref::ARef,
-    transmute::FromBytes,
 };

-use zerocopy::FromBytes as _;
-
 use crate::{
     driver::Bar0,
     firmware::{
@@ -301,7 +298,7 @@ pub(crate) fn fwsec_image(&self) -> &FwSecBiosImage {
 }

 /// PCI Data Structure as defined in PCI Firmware Specification
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, FromBytes)]
 #[repr(C)]
 struct PcirStruct {
     /// PCI Data Structure signature ("PCIR" or "NPDS")
@@ -330,12 +327,9 @@ struct PcirStruct {
     max_runtime_image_len: u16,
 }

-// SAFETY: all bit patterns are valid for `PcirStruct`.
-unsafe impl FromBytes for PcirStruct {}
-
 impl PcirStruct {
     fn new(dev: &device::Device, data: &[u8]) -> Result<Self> {
-        let (pcir, _) = PcirStruct::from_bytes_copy_prefix(data).ok_or(EINVAL)?;
+        let (pcir, _) = PcirStruct::read_from_prefix(data).map_err(|_| EINVAL)?;

         // Signature should be "PCIR" (0x52494350) or "NPDS" (0x5344504e).
         if &pcir.signature != b"PCIR" && &pcir.signature != b"NPDS" {
@@ -371,7 +365,7 @@ fn image_size_bytes(&self) -> usize {
 /// This is the head of the BIT table, that is used to locate the Falcon data. The BIT table (with
 /// its header) is in the [`PciAtBiosImage`] and the falcon data it is pointing to is in the
 /// [`FwSecBiosImage`].
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, FromBytes)]
 #[repr(C)]
 struct BitHeader {
     /// 0h: BIT Header Identifier (BMP=0x7FFF/BIT=0xB8FF)
@@ -390,12 +384,9 @@ struct BitHeader {
     checksum: u8,
 }

-// SAFETY: all bit patterns are valid for `BitHeader`.
-unsafe impl FromBytes for BitHeader {}
-
 impl BitHeader {
     fn new(data: &[u8]) -> Result<Self> {
-        let (header, _) = BitHeader::from_bytes_copy_prefix(data).ok_or(EINVAL)?;
+        let (header, _) = BitHeader::read_from_prefix(data).map_err(|_| EINVAL)?;

         // Check header ID and signature
         if header.id != 0xB8FF || &header.signature != b"BIT\0" {
@@ -533,7 +524,7 @@ fn new(dev: &device::Device, data: &[u8]) -> Result<Self> {
 /// PCI Data Structure. It contains some fields that are redundant with the PCI Data Structure, but
 /// are needed for traversing the BIOS images. It is expected to be present in all BIOS images
 /// except for NBSI images.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, FromBytes)]
 #[repr(C)]
 struct NpdeStruct {
     /// 00h: Signature ("NPDE")
@@ -548,12 +539,9 @@ struct NpdeStruct {
     last_image: u8,
 }

-// SAFETY: all bit patterns are valid for `NpdeStruct`.
-unsafe impl FromBytes for NpdeStruct {}
-
 impl NpdeStruct {
     fn new(dev: &device::Device, data: &[u8]) -> Option<Self> {
-        let (npde, _) = NpdeStruct::from_bytes_copy_prefix(data)?;
+        let (npde, _) = NpdeStruct::read_from_prefix(data).ok()?;

         // Signature should be "NPDE" (0x4544504E).
         if &npde.signature != b"NPDE" {
@@ -845,6 +833,7 @@ fn new(data: &[u8]) -> Result<Self> {
 }

 #[repr(C)]
+#[derive(FromBytes)]
 struct PmuLookupTableHeader {
     version: u8,
     header_len: u8,
@@ -852,9 +841,6 @@ struct PmuLookupTableHeader {
     entry_count: u8,
 }

-// SAFETY: all bit patterns are valid for `PmuLookupTableHeader`.
-unsafe impl FromBytes for PmuLookupTableHeader {}
-
 /// The [`PmuLookupTableEntry`] structure is used to find the [`PmuLookupTableEntry`] for a given
 /// application ID.
 ///
@@ -867,7 +853,7 @@ struct PmuLookupTable {

 impl PmuLookupTable {
     fn new(dev: &device::Device, data: &[u8]) -> Result<Self> {
-        let (header, _) = PmuLookupTableHeader::from_bytes_copy_prefix(data).ok_or(EINVAL)?;
+        let (header, _) = PmuLookupTableHeader::read_from_prefix(data).map_err(|_| EINVAL)?;

         let header_len = usize::from(header.header_len);
         let entry_len = usize::from(header.entry_len);
@@ -1013,15 +999,11 @@ pub(crate) fn header(&self) -> Result<FalconUCodeDesc> {
         let data = self.base.data.get(falcon_ucode_offset..).ok_or(EINVAL)?;
         match ver {
             2 => {
-                let v2 = FalconUCodeDescV2::read_from_prefix(data)
-                    .map_err(|_| EINVAL)?
-                    .0;
+                let (v2, _) = FalconUCodeDescV2::read_from_prefix(data).map_err(|_| EINVAL)?;
                 Ok(FalconUCodeDesc::V2(v2))
             }
             3 => {
-                let v3 = FalconUCodeDescV3::from_bytes_copy_prefix(data)
-                    .ok_or(EINVAL)?
-                    .0;
+                let (v3, _) = FalconUCodeDescV3::read_from_prefix(data).map_err(|_| EINVAL)?;
                 Ok(FalconUCodeDesc::V3(v3))
             }
             _ => {
--
2.47.3