ic_memory/runtime/
layout.rs

1//! Read-only adapter for the documented ic-stable-structures 0.7.2 MGR V1
2//! layout. No ledger or payload reads. Keep the dependency pinned when changing
3//! this adapter; layout changes require a new review, not a fallback decoder.
4use super::RuntimeConstructionError;
5use crate::WASM_PAGE_SIZE_BYTES;
6use ic_platform::stable_structures::Memory;
7
8pub(super) const IDS: usize = 255;
9pub(super) const BUCKET_CAPACITY: u16 = 32_768;
10pub(super) const BUCKETS: usize = BUCKET_CAPACITY as usize;
11pub(super) const HEADER_BYTES: usize = 40 + IDS * 8;
12pub(super) const METADATA_BYTES: usize = HEADER_BYTES + BUCKETS;
13
14///
15/// MemoryManagerLayoutError
16///
17/// Invalid or unsupported persisted manager metadata. No writes are performed
18/// when reporting these failures. Memory implementations must obey [`Memory`].
19///
20
21#[derive(Clone, Copy, Debug, Eq, PartialEq, thiserror::Error)]
22#[non_exhaustive]
23pub enum MemoryManagerLayoutError {
24    /// This adapter supports the little-endian IC/current native layout only.
25    #[error("unsupported big-endian manager layout")]
26    UnsupportedByteOrder,
27    /// The persisted bucket size is zero.
28    #[error("persisted bucket size is zero")]
29    ZeroBucketSize,
30    /// Reserved header fields are not recognized by this adapter.
31    #[error("nonzero reserved manager header bytes")]
32    ReservedHeader,
33    /// The allocated count exceeds the finite bucket table.
34    #[error("allocated bucket count {count} exceeds 32768")]
35    BucketCount { count: u16 },
36    /// Allocated buckets must be a dense prefix and all later entries unused.
37    #[error("invalid bucket table entry at index {index}")]
38    BucketTable { index: u16 },
39    /// Virtual extent disagrees with the number of assigned buckets.
40    #[error("virtual extent and bucket count disagree for memory ID {id}")]
41    VirtualExtent { id: u8 },
42    /// Backing memory does not cover every assigned bucket.
43    #[error("physical extent {physical_pages} pages is below assigned end {required_pages}")]
44    TruncatedBacking {
45        physical_pages: u64,
46        required_pages: u64,
47    },
48    /// Backing size cannot be represented in bytes.
49    #[error("backing memory extent overflows bytes")]
50    ExtentOverflow,
51    /// A live manager's cached state differs from persisted metadata.
52    #[error("persisted manager metadata differs from runtime authority")]
53    RuntimeMismatch,
54}
55
56pub(super) struct Layout {
57    pub metadata: [u8; METADATA_BYTES],
58    pub physical_pages: u64,
59    pub bucket_pages: u16,
60    pub allocated_buckets: u16,
61    pub pages: [u64; IDS],
62    pub buckets: [u16; IDS],
63}
64
65// Exact expected metadata, never refreshed from foreign mutations. The pinned
66// manager is still the only writer. Growth projects its known header/table
67// edits into this read-only authority before comparing the persisted result.
68pub(super) struct ManagerAuthority {
69    expected: Box<[u8]>,
70    poisoned: std::cell::Cell<bool>,
71}
72
73impl ManagerAuthority {
74    pub fn capture(memory: &impl Memory) -> Self {
75        let mut expected = vec![0; METADATA_BYTES].into_boxed_slice();
76        memory.read(0, &mut expected);
77        Self {
78            expected,
79            poisoned: std::cell::Cell::new(false),
80        }
81    }
82
83    pub fn allocated_buckets(&self) -> u16 {
84        u16::from_le_bytes([self.expected[4], self.expected[5]])
85    }
86
87    pub fn verify(&self, memory: &impl Memory) -> Result<(), MemoryManagerLayoutError> {
88        if self.poisoned.get() {
89            return Err(MemoryManagerLayoutError::RuntimeMismatch);
90        }
91        #[expect(
92            clippy::large_stack_arrays,
93            reason = "fixed manager metadata bound, no payload reads or heap allocation"
94        )]
95        let mut actual = [0; METADATA_BYTES];
96        let required_pages = 1 + u64::from(self.allocated_buckets())
97            * u64::from(u16::from_le_bytes([self.expected[6], self.expected[7]]));
98        if memory.size() < required_pages {
99            self.poisoned.set(true);
100            return Err(MemoryManagerLayoutError::RuntimeMismatch);
101        }
102        memory.read(0, &mut actual);
103        self.verify_observed(&actual)
104    }
105
106    pub fn poison(&self) {
107        self.poisoned.set(true);
108    }
109
110    pub fn verify_observed(&self, actual: &[u8]) -> Result<(), MemoryManagerLayoutError> {
111        // MGR V1's complete 34848-byte image is an exact number of words.
112        // Explicit word comparison avoids Wasm's byte-at-a-time memcmp while
113        // preserving every byte of the admission boundary, including unused IDs.
114        #[cfg(target_arch = "wasm32")]
115        let matches = {
116            let (actual_words, actual_tail) = actual.as_chunks::<8>();
117            let (expected_words, expected_tail) = self.expected.as_chunks::<8>();
118            actual.len() == METADATA_BYTES
119                && self.expected.len() == METADATA_BYTES
120                && actual_tail.is_empty()
121                && expected_tail.is_empty()
122                && actual_words
123                    .iter()
124                    .zip(expected_words)
125                    .all(|(actual, expected)| {
126                        u64::from_le_bytes(*actual) == u64::from_le_bytes(*expected)
127                    })
128        };
129        // Native slice equality uses the optimized host comparator, including
130        // in debug test builds. Both paths compare the complete exact image.
131        #[cfg(not(target_arch = "wasm32"))]
132        let matches = actual.len() == METADATA_BYTES && actual == self.expected.as_ref();
133        if self.poisoned.get() || !matches {
134            self.poisoned.set(true);
135            return Err(MemoryManagerLayoutError::RuntimeMismatch);
136        }
137        Ok(())
138    }
139
140    pub fn record_growth(&mut self, id: u8, pages: u64, allocated: u16) {
141        let old = usize::from(self.allocated_buckets());
142        self.expected[HEADER_BYTES + old..HEADER_BYTES + usize::from(allocated)].fill(id);
143        self.expected[4..6].copy_from_slice(&allocated.to_le_bytes());
144        let offset = 40 + usize::from(id) * 8;
145        self.expected[offset..offset + 8].copy_from_slice(&pages.to_le_bytes());
146    }
147}
148
149pub(super) fn read<M: Memory>(memory: &M) -> Result<Layout, RuntimeConstructionError> {
150    if cfg!(target_endian = "big") {
151        return Err(MemoryManagerLayoutError::UnsupportedByteOrder.into());
152    }
153    let physical_pages = memory.size();
154    physical_pages
155        .checked_mul(WASM_PAGE_SIZE_BYTES)
156        .ok_or(MemoryManagerLayoutError::ExtentOverflow)?;
157    // The caller handles empty memory. Even one page covers all metadata.
158    if physical_pages == 0 {
159        return Err(MemoryManagerLayoutError::TruncatedBacking {
160            physical_pages,
161            required_pages: 1,
162        }
163        .into());
164    }
165    #[expect(
166        clippy::large_stack_arrays,
167        reason = "bounded manager image is also the diagnostic authority observation"
168    )]
169    let mut metadata = [0; METADATA_BYTES];
170    let (header, table) = metadata.split_at_mut(HEADER_BYTES);
171    memory.read(0, header);
172    let observed_magic = [header[0], header[1], header[2]];
173    if observed_magic != *b"MGR" {
174        return Err(RuntimeConstructionError::ForeignMemory { observed_magic });
175    }
176    if header[3] != 1 {
177        return Err(RuntimeConstructionError::UnsupportedMemoryManagerVersion {
178            observed: header[3],
179            supported: 1,
180        });
181    }
182    if header[8..40].iter().any(|byte| *byte != 0) {
183        return Err(MemoryManagerLayoutError::ReservedHeader.into());
184    }
185    let allocated_buckets = u16::from_le_bytes([header[4], header[5]]);
186    let bucket_pages = u16::from_le_bytes([header[6], header[7]]);
187    if bucket_pages == 0 {
188        return Err(MemoryManagerLayoutError::ZeroBucketSize.into());
189    }
190    if usize::from(allocated_buckets) > BUCKETS {
191        return Err(MemoryManagerLayoutError::BucketCount {
192            count: allocated_buckets,
193        }
194        .into());
195    }
196    let required_pages = 1 + u64::from(allocated_buckets) * u64::from(bucket_pages);
197    if physical_pages < required_pages {
198        return Err(MemoryManagerLayoutError::TruncatedBacking {
199            physical_pages,
200            required_pages,
201        }
202        .into());
203    }
204    // Fixed local buffer and read bound, independent of physical size/history.
205    memory.read(HEADER_BYTES as u64, table);
206    let mut buckets = [0_u16; IDS];
207    for (index, id) in (0_u16..32_768).zip(table.iter().copied()) {
208        if (index < allocated_buckets) != (id != 255) {
209            return Err(MemoryManagerLayoutError::BucketTable { index }.into());
210        }
211        if id != 255 {
212            buckets[usize::from(id)] += 1;
213        }
214    }
215    let mut pages = [0; IDS];
216    for (id, value) in (0_u8..255).zip(&mut pages) {
217        let offset = 40 + usize::from(id) * 8;
218        *value = u64::from_le_bytes(header[offset..offset + 8].try_into().expect("eight bytes"));
219        if value.div_ceil(u64::from(bucket_pages)) != u64::from(buckets[usize::from(id)]) {
220            return Err(MemoryManagerLayoutError::VirtualExtent { id }.into());
221        }
222    }
223    Ok(Layout {
224        metadata,
225        physical_pages,
226        bucket_pages,
227        allocated_buckets,
228        pages,
229        buckets,
230    })
231}
ic_memory/runtime/layout.rs

ic_memory/runtime/
layout.rs
