acpi/rsdp.rs
1use crate::{AcpiError, AcpiHandler, AcpiResult, PhysicalMapping};
2use core::{mem, ops::Range, slice, str};
3
4/// The size in bytes of the ACPI 1.0 RSDP.
5const RSDP_V1_LENGTH: usize = 20;
6/// The total size in bytes of the RSDP fields introduced in ACPI 2.0.
7const RSDP_V2_EXT_LENGTH: usize = mem::size_of::<Rsdp>() - RSDP_V1_LENGTH;
8
9/// The first structure found in ACPI. It just tells us where the RSDT is.
10///
11/// On BIOS systems, it is either found in the first 1KiB of the Extended Bios Data Area, or between `0x000e0000`
12/// and `0x000fffff`. The signature is always on a 16 byte boundary. On (U)EFI, it may not be located in these
13/// locations, and so an address should be found in the EFI configuration table instead.
14///
15/// The recommended way of locating the RSDP is to let the bootloader do it - Multiboot2 can pass a
16/// tag with the physical address of it. If this is not possible, a manual scan can be done.
17///
18/// If `revision > 0`, (the hardware ACPI version is Version 2.0 or greater), the RSDP contains
19/// some new fields. For ACPI Version 1.0, these fields are not valid and should not be accessed.
20/// For ACPI Version 2.0+, `xsdt_address` should be used (truncated to `u32` on x86) instead of
21/// `rsdt_address`.
22#[derive(Clone, Copy, Debug)]
23#[repr(C, packed)]
24pub struct Rsdp {
25 signature: [u8; 8],
26 checksum: u8,
27 oem_id: [u8; 6],
28 revision: u8,
29 rsdt_address: u32,
30
31 /*
32 * These fields are only valid for ACPI Version 2.0 and greater
33 */
34 length: u32,
35 xsdt_address: u64,
36 ext_checksum: u8,
37 reserved: [u8; 3],
38}
39
40impl Rsdp {
41 /// This searches for a RSDP on BIOS systems.
42 ///
43 /// ### Safety
44 /// This function probes memory in three locations:
45 /// - It reads a word from `40:0e` to locate the EBDA.
46 /// - The first 1KiB of the EBDA (Extended BIOS Data Area).
47 /// - The BIOS memory area at `0xe0000..=0xfffff`.
48 ///
49 /// This should be fine on all BIOS systems. However, UEFI platforms are free to put the RSDP wherever they
50 /// please, so this won't always find the RSDP. Further, prodding these memory locations may have unintended
51 /// side-effects. On UEFI systems, the RSDP should be found in the Configuration Table, using two GUIDs:
52 /// - ACPI v1.0 structures use `eb9d2d30-2d88-11d3-9a16-0090273fc14d`.
53 /// - ACPI v2.0 or later structures use `8868e871-e4f1-11d3-bc22-0080c73c8881`.
54 /// You should search the entire table for the v2.0 GUID before searching for the v1.0 one.
55 pub unsafe fn search_for_on_bios<H>(handler: H) -> AcpiResult<PhysicalMapping<H, Rsdp>>
56 where
57 H: AcpiHandler,
58 {
59 let rsdp_address = find_search_areas(handler.clone()).iter().find_map(|area| {
60 // Map the search area for the RSDP followed by `RSDP_V2_EXT_LENGTH` bytes so an ACPI 1.0 RSDP at the
61 // end of the area can be read as an `Rsdp` (which always has the size of an ACPI 2.0 RSDP)
62 let mapping = unsafe {
63 handler.map_physical_region::<u8>(area.start, area.end - area.start + RSDP_V2_EXT_LENGTH)
64 };
65
66 let extended_area_bytes =
67 unsafe { slice::from_raw_parts(mapping.virtual_start().as_ptr(), mapping.region_length()) };
68
69 // Search `Rsdp`-sized windows at 16-byte boundaries relative to the base of the area (which is also
70 // aligned to 16 bytes due to the implementation of `find_search_areas`)
71 extended_area_bytes.windows(mem::size_of::<Rsdp>()).step_by(16).find_map(|maybe_rsdp_bytes_slice| {
72 let maybe_rsdp_virt_ptr = maybe_rsdp_bytes_slice.as_ptr().cast::<Rsdp>();
73 let maybe_rsdp_phys_start = maybe_rsdp_virt_ptr as usize
74 - mapping.virtual_start().as_ptr() as usize
75 + mapping.physical_start();
76 // SAFETY: `maybe_rsdp_virt_ptr` points to an aligned, readable `Rsdp`-sized value, and the `Rsdp`
77 // struct's fields are always initialized.
78 let maybe_rsdp = unsafe { &*maybe_rsdp_virt_ptr };
79
80 match maybe_rsdp.validate() {
81 Ok(()) => Some(maybe_rsdp_phys_start),
82 Err(AcpiError::RsdpIncorrectSignature) => None,
83 Err(err) => {
84 log::warn!("Invalid RSDP found at {:#x}: {:?}", maybe_rsdp_phys_start, err);
85 None
86 }
87 }
88 })
89 });
90
91 match rsdp_address {
92 Some(address) => {
93 let rsdp_mapping = unsafe { handler.map_physical_region::<Rsdp>(address, mem::size_of::<Rsdp>()) };
94 Ok(rsdp_mapping)
95 }
96 None => Err(AcpiError::NoValidRsdp),
97 }
98 }
99
100 /// Checks that:
101 /// 1) The signature is correct
102 /// 2) The checksum is correct
103 /// 3) For Version 2.0+, that the extension checksum is correct
104 pub fn validate(&self) -> AcpiResult<()> {
105 // Check the signature
106 if self.signature != RSDP_SIGNATURE {
107 return Err(AcpiError::RsdpIncorrectSignature);
108 }
109
110 // Check the OEM id is valid UTF8 (allows use of unwrap)
111 if str::from_utf8(&self.oem_id).is_err() {
112 return Err(AcpiError::RsdpInvalidOemId);
113 }
114
115 /*
116 * `self.length` doesn't exist on ACPI version 1.0, so we mustn't rely on it. Instead,
117 * check for version 1.0 and use a hard-coded length instead.
118 */
119 let length = if self.revision > 0 {
120 // For Version 2.0+, include the number of bytes specified by `length`
121 self.length as usize
122 } else {
123 RSDP_V1_LENGTH
124 };
125
126 let bytes = unsafe { slice::from_raw_parts(self as *const Rsdp as *const u8, length) };
127 let sum = bytes.iter().fold(0u8, |sum, &byte| sum.wrapping_add(byte));
128
129 if sum != 0 {
130 return Err(AcpiError::RsdpInvalidChecksum);
131 }
132
133 Ok(())
134 }
135
136 pub fn signature(&self) -> [u8; 8] {
137 self.signature
138 }
139
140 pub fn checksum(&self) -> u8 {
141 self.checksum
142 }
143
144 pub fn oem_id(&self) -> &str {
145 str::from_utf8(&self.oem_id).unwrap()
146 }
147
148 pub fn revision(&self) -> u8 {
149 self.revision
150 }
151
152 pub fn rsdt_address(&self) -> u32 {
153 self.rsdt_address
154 }
155
156 pub fn length(&self) -> u32 {
157 assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
158 self.length
159 }
160
161 pub fn xsdt_address(&self) -> u64 {
162 assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
163 self.xsdt_address
164 }
165
166 pub fn ext_checksum(&self) -> u8 {
167 assert!(self.revision > 0, "Tried to read extended RSDP field with ACPI Version 1.0");
168 self.ext_checksum
169 }
170}
171
172/// Find the areas we should search for the RSDP in.
173fn find_search_areas<H>(handler: H) -> [Range<usize>; 2]
174where
175 H: AcpiHandler,
176{
177 /*
178 * Read the base address of the EBDA from its location in the BDA (BIOS Data Area). Not all BIOSs fill this out
179 * unfortunately, so we might not get a sensible result. We shift it left 4, as it's a segment address.
180 */
181 let ebda_start_mapping =
182 unsafe { handler.map_physical_region::<u16>(EBDA_START_SEGMENT_PTR, mem::size_of::<u16>()) };
183 let ebda_start = (*ebda_start_mapping as usize) << 4;
184
185 [
186 /*
187 * The main BIOS area below 1MiB. In practice, from my [Restioson's] testing, the RSDP is more often here
188 * than the EBDA. We also don't want to search the entire possibele EBDA range, if we've failed to find it
189 * from the BDA.
190 */
191 RSDP_BIOS_AREA_START..(RSDP_BIOS_AREA_END + 1),
192 // Check if base segment ptr is in valid range for EBDA base
193 if (EBDA_EARLIEST_START..EBDA_END).contains(&ebda_start) {
194 // First KiB of EBDA
195 ebda_start..ebda_start + 1024
196 } else {
197 // We don't know where the EBDA starts, so just search the largest possible EBDA
198 EBDA_EARLIEST_START..(EBDA_END + 1)
199 },
200 ]
201}
202
203/// This (usually!) contains the base address of the EBDA (Extended Bios Data Area), shifted right by 4
204const EBDA_START_SEGMENT_PTR: usize = 0x40e;
205/// The earliest (lowest) memory address an EBDA (Extended Bios Data Area) can start
206const EBDA_EARLIEST_START: usize = 0x80000;
207/// The end of the EBDA (Extended Bios Data Area)
208const EBDA_END: usize = 0x9ffff;
209/// The start of the main BIOS area below 1MiB in which to search for the RSDP (Root System Description Pointer)
210const RSDP_BIOS_AREA_START: usize = 0xe0000;
211/// The end of the main BIOS area below 1MiB in which to search for the RSDP (Root System Description Pointer)
212const RSDP_BIOS_AREA_END: usize = 0xfffff;
213/// The RSDP (Root System Description Pointer)'s signature, "RSD PTR " (note trailing space)
214const RSDP_SIGNATURE: [u8; 8] = *b"RSD PTR ";