src/rsdp.rs - platform/external/rust/crates/acpi - Git at Google

 use crate::{AcpiError, AcpiHandler, AcpiResult, PhysicalMapping};
 use core::{mem, ops::Range, slice, str};

 /// The size in bytes of the ACPI 1.0 RSDP.
 const RSDP_V1_LENGTH: usize = 20;
 /// The total size in bytes of the RSDP fields introduced in ACPI 2.0.
 const RSDP_V2_EXT_LENGTH: usize = mem::size_of::<Rsdp>() - RSDP_V1_LENGTH;

 /// The first structure found in ACPI. It just tells us where the RSDT is.
 ///
 /// On BIOS systems, it is either found in the first 1KiB of the Extended Bios Data Area, or between `0x000e0000`
 /// and `0x000fffff`. The signature is always on a 16 byte boundary. On (U)EFI, it may not be located in these
 /// locations, and so an address should be found in the EFI configuration table instead.
 ///
 /// The recommended way of locating the RSDP is to let the bootloader do it - Multiboot2 can pass a
 /// tag with the physical address of it. If this is not possible, a manual scan can be done.
 ///
 /// If `revision > 0`, (the hardware ACPI version is Version 2.0 or greater), the RSDP contains
 /// some new fields. For ACPI Version 1.0, these fields are not valid and should not be accessed.
 /// For ACPI Version 2.0+, `xsdt_address` should be used (truncated to `u32` on x86) instead of
 /// `rsdt_address`.
 #[derive(Clone, Copy, Debug)]
 #[repr(C, packed)]
 pub struct Rsdp {
     signature: [u8; 8],
     checksum: u8,
     oem_id: [u8; 6],
     revision: u8,
     rsdt_address: u32,

     /*
      * These fields are only valid for ACPI Version 2.0 and greater
      */
     length: u32,
     xsdt_address: u64,
     ext_checksum: u8,
     reserved: [u8; 3],
 }

 impl Rsdp {
     /// This searches for a RSDP on BIOS systems.
     ///
     /// ### Safety
     /// This function probes memory in three locations:
     ///    - It reads a word from `40:0e` to locate the EBDA.
     ///    - The first 1KiB of the EBDA (Extended BIOS Data Area).
     ///    - The BIOS memory area at `0xe0000..=0xfffff`.
     ///
     /// This should be fine on all BIOS systems. However, UEFI platforms are free to put the RSDP wherever they
     /// please, so this won't always find the RSDP. Further, prodding these memory locations may have unintended
     /// side-effects. On UEFI systems, the RSDP should be found in the Configuration Table, using two GUIDs:
     ///     - ACPI v1.0 structures use `eb9d2d30-2d88-11d3-9a16-0090273fc14d`.
     ///     - ACPI v2.0 or later structures use `8868e871-e4f1-11d3-bc22-0080c73c8881`.
     /// You should search the entire table for the v2.0 GUID before searching for the v1.0 one.
     pub unsafe fn search_for_on_bios<H>(handler: H) -> AcpiResult<PhysicalMapping<H, Rsdp>>
     where
         H: AcpiHandler,
     {
         let rsdp_address = find_search_areas(handler.clone()).iter().find_map(|area| {
             // Map the search area for the RSDP followed by `RSDP_V2_EXT_LENGTH` bytes so an ACPI 1.0 RSDP at the
             // end of the area can be read as an `Rsdp` (which always has the size of an ACPI 2.0 RSDP)
             let mapping = unsafe {
                 handler.map_physical_region::<u8>(area.start, area.end - area.start + RSDP_V2_EXT_LENGTH)
             };

             let extended_area_bytes =
                 unsafe { slice::from_raw_parts(mapping.virtual_start().as_ptr(), mapping.region_length()) };

             // Search `Rsdp`-sized windows at 16-byte boundaries relative to the base of the area (which is also
             // aligned to 16 bytes due to the implementation of `find_search_areas`)
             extended_area_bytes.windows(mem::size_of::<Rsdp>()).step_by(16).find_map(|maybe_rsdp_bytes_slice| {
                 let maybe_rsdp_virt_ptr = maybe_rsdp_bytes_slice.as_ptr().cast::<Rsdp>();
                 let maybe_rsdp_phys_start = maybe_rsdp_virt_ptr as usize
                     - mapping.virtual_start().as_ptr() as usize
                     + mapping.physical_start();
                 // SAFETY: `maybe_rsdp_virt_ptr` points to an aligned, readable `Rsdp`-sized value, and the `Rsdp`
                 // struct's fields are always initialized.
                 let maybe_rsdp = unsafe { &*maybe_rsdp_virt_ptr };

                 match maybe_rsdp.validate() {
                     Ok(()) => Some(maybe_rsdp_phys_start),
                     Err(AcpiError::RsdpIncorrectSignature) => None,
                     Err(err) => {
                         log::warn!("Invalid RSDP found at {:#x}: {:?}", maybe_rsdp_phys_start, err);
                         None
                     }
                 }
             })
         });

         match rsdp_address {
             Some(address) => {
                 let rsdp_mapping = unsafe { handler.map_physical_region::<Rsdp>(address, mem::size_of::<Rsdp>()) };
                 Ok(rsdp_mapping)
             }
             None => Err(AcpiError::NoValidRsdp),
         }
     }

     /// Checks that:
     ///     1) The signature is correct
     ///     2) The checksum is correct
     ///     3) For Version 2.0+, that the extension checksum is correct
     pub fn validate(&self) -> AcpiResult<()> {
         // Check the signature
         if self.signature != RSDP_SIGNATURE {
             return Err(AcpiError::RsdpIncorrectSignature);
         }

         // Check the OEM id is valid UTF8 (allows use of unwrap)
         if str::from_utf8(&self.oem_id).is_err() {
             return Err(AcpiError::RsdpInvalidOemId);
         }

         /*
          * `self.length` doesn't exist on ACPI version 1.0, so we mustn't rely on it. Instead,
          * check for version 1.0 and use a hard-coded length instead.
          */
         let length = if self.revision > 0 {
             // For Version 2.0+, include the number of bytes specified by `length`
             self.length as usize
         } else {
             RSDP_V1_LENGTH
         };

         let bytes = unsafe { slice::from_raw_parts(self as *const Rsdp as *const u8, length) };
         let sum = bytes.iter().fold(0u8, |sum, &byte| sum.wrapping_add(byte));

         if sum != 0 {
             return Err(AcpiError::RsdpInvalidChecksum);
         }

         Ok(())
     }

     pub fn signature(&self) -> [u8; 8] {
         self.signature
     }

     pub fn checksum(&self) -> u8 {
         self.checksum
     }

     pub fn oem_id(&self) -> &str {
         str::from_utf8(&self.oem_id).unwrap()
     }

     pub fn revision(&self) -> u8 {
         self.revision
     }

     pub fn rsdt_address(&self) -> u32 {
         self.rsdt_address
     }

     pub fn length(&self) -> u32 {
         assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
         self.length
     }

     pub fn xsdt_address(&self) -> u64 {
         assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
         self.xsdt_address
     }

     pub fn ext_checksum(&self) -> u8 {
         assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
         self.ext_checksum
     }
 }

 /// Find the areas we should search for the RSDP in.
 fn find_search_areas<H>(handler: H) -> [Range<usize>; 2]
 where
     H: AcpiHandler,
 {
     /*
      * Read the base address of the EBDA from its location in the BDA (BIOS Data Area). Not all BIOSs fill this out
      * unfortunately, so we might not get a sensible result. We shift it left 4, as it's a segment address.
      */
     let ebda_start_mapping =
         unsafe { handler.map_physical_region::<u16>(EBDA_START_SEGMENT_PTR, mem::size_of::<u16>()) };
     let ebda_start = (*ebda_start_mapping as usize) << 4;

     [
         /*
          * The main BIOS area below 1MiB. In practice, from my [Restioson's] testing, the RSDP is more often here
          * than the EBDA. We also don't want to search the entire possibele EBDA range, if we've failed to find it
          * from the BDA.
          */
         RSDP_BIOS_AREA_START..(RSDP_BIOS_AREA_END + 1),
         // Check if base segment ptr is in valid range for EBDA base
         if (EBDA_EARLIEST_START..EBDA_END).contains(&ebda_start) {
             // First KiB of EBDA
             ebda_start..ebda_start + 1024
         } else {
             // We don't know where the EBDA starts, so just search the largest possible EBDA
             EBDA_EARLIEST_START..(EBDA_END + 1)
         },
     ]
 }

 /// This (usually!) contains the base address of the EBDA (Extended Bios Data Area), shifted right by 4
 const EBDA_START_SEGMENT_PTR: usize = 0x40e;
 /// The earliest (lowest) memory address an EBDA (Extended Bios Data Area) can start
 const EBDA_EARLIEST_START: usize = 0x80000;
 /// The end of the EBDA (Extended Bios Data Area)
 const EBDA_END: usize = 0x9ffff;
 /// The start of the main BIOS area below 1MiB in which to search for the RSDP (Root System Description Pointer)
 const RSDP_BIOS_AREA_START: usize = 0xe0000;
 /// The end of the main BIOS area below 1MiB in which to search for the RSDP (Root System Description Pointer)
 const RSDP_BIOS_AREA_END: usize = 0xfffff;
 /// The RSDP (Root System Description Pointer)'s signature, "RSD PTR " (note trailing space)
 const RSDP_SIGNATURE: [u8; 8] = *b"RSD PTR ";
	use crate::{AcpiError, AcpiHandler, AcpiResult, PhysicalMapping};
	use core::{mem, ops::Range, slice, str};

	/// The size in bytes of the ACPI 1.0 RSDP.
	const RSDP_V1_LENGTH: usize = 20;
	/// The total size in bytes of the RSDP fields introduced in ACPI 2.0.
	const RSDP_V2_EXT_LENGTH: usize = mem::size_of::<Rsdp>() - RSDP_V1_LENGTH;

	/// The first structure found in ACPI. It just tells us where the RSDT is.
	///
	/// On BIOS systems, it is either found in the first 1KiB of the Extended Bios Data Area, or between `0x000e0000`
	/// and `0x000fffff`. The signature is always on a 16 byte boundary. On (U)EFI, it may not be located in these
	/// locations, and so an address should be found in the EFI configuration table instead.
	///
	/// The recommended way of locating the RSDP is to let the bootloader do it - Multiboot2 can pass a
	/// tag with the physical address of it. If this is not possible, a manual scan can be done.
	///
	/// If `revision > 0`, (the hardware ACPI version is Version 2.0 or greater), the RSDP contains
	/// some new fields. For ACPI Version 1.0, these fields are not valid and should not be accessed.
	/// For ACPI Version 2.0+, `xsdt_address` should be used (truncated to `u32` on x86) instead of
	/// `rsdt_address`.
	#[derive(Clone, Copy, Debug)]
	#[repr(C, packed)]
	pub struct Rsdp {
	signature: [u8; 8],
	checksum: u8,
	oem_id: [u8; 6],
	revision: u8,
	rsdt_address: u32,

	/*
	* These fields are only valid for ACPI Version 2.0 and greater
	*/
	length: u32,
	xsdt_address: u64,
	ext_checksum: u8,
	reserved: [u8; 3],
	}

	impl Rsdp {
	/// This searches for a RSDP on BIOS systems.
	///
	/// ### Safety
	/// This function probes memory in three locations:
	/// - It reads a word from `40:0e` to locate the EBDA.
	/// - The first 1KiB of the EBDA (Extended BIOS Data Area).
	/// - The BIOS memory area at `0xe0000..=0xfffff`.
	///
	/// This should be fine on all BIOS systems. However, UEFI platforms are free to put the RSDP wherever they
	/// please, so this won't always find the RSDP. Further, prodding these memory locations may have unintended
	/// side-effects. On UEFI systems, the RSDP should be found in the Configuration Table, using two GUIDs:
	/// - ACPI v1.0 structures use `eb9d2d30-2d88-11d3-9a16-0090273fc14d`.
	/// - ACPI v2.0 or later structures use `8868e871-e4f1-11d3-bc22-0080c73c8881`.
	/// You should search the entire table for the v2.0 GUID before searching for the v1.0 one.
	pub unsafe fn search_for_on_bios<H>(handler: H) -> AcpiResult<PhysicalMapping<H, Rsdp>>
	where
	H: AcpiHandler,
	{
	let rsdp_address = find_search_areas(handler.clone()).iter().find_map(\|area\| {
	// Map the search area for the RSDP followed by `RSDP_V2_EXT_LENGTH` bytes so an ACPI 1.0 RSDP at the
	// end of the area can be read as an `Rsdp` (which always has the size of an ACPI 2.0 RSDP)
	let mapping = unsafe {
	handler.map_physical_region::<u8>(area.start, area.end - area.start + RSDP_V2_EXT_LENGTH)
	};

	let extended_area_bytes =
	unsafe { slice::from_raw_parts(mapping.virtual_start().as_ptr(), mapping.region_length()) };

	// Search `Rsdp`-sized windows at 16-byte boundaries relative to the base of the area (which is also
	// aligned to 16 bytes due to the implementation of `find_search_areas`)
	extended_area_bytes.windows(mem::size_of::<Rsdp>()).step_by(16).find_map(\|maybe_rsdp_bytes_slice\| {
	let maybe_rsdp_virt_ptr = maybe_rsdp_bytes_slice.as_ptr().cast::<Rsdp>();
	let maybe_rsdp_phys_start = maybe_rsdp_virt_ptr as usize
	- mapping.virtual_start().as_ptr() as usize
	+ mapping.physical_start();
	// SAFETY: `maybe_rsdp_virt_ptr` points to an aligned, readable `Rsdp`-sized value, and the `Rsdp`
	// struct's fields are always initialized.
	let maybe_rsdp = unsafe { &*maybe_rsdp_virt_ptr };

	match maybe_rsdp.validate() {
	Ok(()) => Some(maybe_rsdp_phys_start),
	Err(AcpiError::RsdpIncorrectSignature) => None,
	Err(err) => {
	log::warn!("Invalid RSDP found at {:#x}: {:?}", maybe_rsdp_phys_start, err);
	None
	}
	}
	})
	});

	match rsdp_address {
	Some(address) => {
	let rsdp_mapping = unsafe { handler.map_physical_region::<Rsdp>(address, mem::size_of::<Rsdp>()) };
	Ok(rsdp_mapping)
	}
	None => Err(AcpiError::NoValidRsdp),
	}
	}

	/// Checks that:
	/// 1) The signature is correct
	/// 2) The checksum is correct
	/// 3) For Version 2.0+, that the extension checksum is correct
	pub fn validate(&self) -> AcpiResult<()> {
	// Check the signature
	if self.signature != RSDP_SIGNATURE {
	return Err(AcpiError::RsdpIncorrectSignature);
	}

	// Check the OEM id is valid UTF8 (allows use of unwrap)
	if str::from_utf8(&self.oem_id).is_err() {
	return Err(AcpiError::RsdpInvalidOemId);
	}

	/*
	* `self.length` doesn't exist on ACPI version 1.0, so we mustn't rely on it. Instead,
	* check for version 1.0 and use a hard-coded length instead.
	*/
	let length = if self.revision > 0 {
	// For Version 2.0+, include the number of bytes specified by `length`
	self.length as usize
	} else {
	RSDP_V1_LENGTH
	};

	let bytes = unsafe { slice::from_raw_parts(self as const Rsdp as const u8, length) };
	let sum = bytes.iter().fold(0u8, \|sum, &byte\| sum.wrapping_add(byte));

	if sum != 0 {
	return Err(AcpiError::RsdpInvalidChecksum);
	}

	Ok(())
	}

	pub fn signature(&self) -> [u8; 8] {
	self.signature
	}

	pub fn checksum(&self) -> u8 {
	self.checksum
	}

	pub fn oem_id(&self) -> &str {
	str::from_utf8(&self.oem_id).unwrap()
	}

	pub fn revision(&self) -> u8 {
	self.revision
	}

	pub fn rsdt_address(&self) -> u32 {
	self.rsdt_address
	}

	pub fn length(&self) -> u32 {
	assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
	self.length
	}

	pub fn xsdt_address(&self) -> u64 {
	assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
	self.xsdt_address
	}

	pub fn ext_checksum(&self) -> u8 {
	assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
	self.ext_checksum
	}
	}

	/// Find the areas we should search for the RSDP in.
	fn find_search_areas<H>(handler: H) -> [Range<usize>; 2]
	where
	H: AcpiHandler,
	{
	/*
	* Read the base address of the EBDA from its location in the BDA (BIOS Data Area). Not all BIOSs fill this out
	* unfortunately, so we might not get a sensible result. We shift it left 4, as it's a segment address.
	*/
	let ebda_start_mapping =
	unsafe { handler.map_physical_region::<u16>(EBDA_START_SEGMENT_PTR, mem::size_of::<u16>()) };
	let ebda_start = (*ebda_start_mapping as usize) << 4;

	[
	/*
	* The main BIOS area below 1MiB. In practice, from my [Restioson's] testing, the RSDP is more often here
	* than the EBDA. We also don't want to search the entire possibele EBDA range, if we've failed to find it
	* from the BDA.
	*/
	RSDP_BIOS_AREA_START..(RSDP_BIOS_AREA_END + 1),
	// Check if base segment ptr is in valid range for EBDA base
	if (EBDA_EARLIEST_START..EBDA_END).contains(&ebda_start) {
	// First KiB of EBDA
	ebda_start..ebda_start + 1024
	} else {
	// We don't know where the EBDA starts, so just search the largest possible EBDA
	EBDA_EARLIEST_START..(EBDA_END + 1)
	},
	]
	}

	/// This (usually!) contains the base address of the EBDA (Extended Bios Data Area), shifted right by 4
	const EBDA_START_SEGMENT_PTR: usize = 0x40e;
	/// The earliest (lowest) memory address an EBDA (Extended Bios Data Area) can start
	const EBDA_EARLIEST_START: usize = 0x80000;
	/// The end of the EBDA (Extended Bios Data Area)
	const EBDA_END: usize = 0x9ffff;
	/// The start of the main BIOS area below 1MiB in which to search for the RSDP (Root System Description Pointer)
	const RSDP_BIOS_AREA_START: usize = 0xe0000;
	/// The end of the main BIOS area below 1MiB in which to search for the RSDP (Root System Description Pointer)
	const RSDP_BIOS_AREA_END: usize = 0xfffff;
	/// The RSDP (Root System Description Pointer)'s signature, "RSD PTR " (note trailing space)
	const RSDP_SIGNATURE: [u8; 8] = *b"RSD PTR ";