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fix(boot): avoid Secure Boot low-memory reservations #604

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Merged
hodgesds merged 1 commit into from
Oct 12, 2026
Merged

fix(boot): avoid Secure Boot low-memory reservations #604

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11 changes: 6 additions & 5 deletions build/linker/x86_64.ld
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Expand Up @@ -4,15 +4,16 @@

ENTRY(_start)

/* 16 MiB. Modern UEFI firmware on x86_64 (OVMF on QEMU, real-world
* EDK2 builds, Lenovo / Dell / HP firmware) typically reserves the
* 0–16 MiB range for its own code, ACPI tables, and BootServices
* data. Loading the kernel above that line keeps the .data + .bss
/* 32 MiB. Modern UEFI firmware on x86_64 (OVMF on QEMU, real-world
* EDK2 builds, Lenovo / Dell / HP firmware) can reserve low memory for
* code, ACPI tables, BootServices data, and SMM communication buffers.
* Secure Boot OVMF with SMM reserves through 26 MiB. Loading the kernel
* above that line keeps the .data + .bss
* LOAD segment (~38 MiB once the 32-MiB static heap arena is
* accounted for) inside contiguous EfiConventionalMemory. The PVH
* direct-boot path (QEMU `-kernel`) honours the same ELF p_paddr,
* so this works for both protocols. */
KERNEL_LOAD_BASE = 0x1000000;
KERNEL_LOAD_BASE = 0x2000000;
KERNEL_VIRT_BASE = 0xFFFFFFFF80000000;

/* VA span reserved for the kernel image. The module text window begins
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3 changes: 3 additions & 0 deletions build/specification/spec.md
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Expand Up @@ -239,6 +239,9 @@ and CI compiler-cache integration.
- Kernel ELFs on both architectures carry a deterministic SHA-1 GNU build-ID;
linker symbols `__build_id_note_start` and `__build_id_note_end` delimit the
retained note for `/sys/kernel/notes`.
- The x86_64 ELF uses a 32 MiB physical load base for both PVH and
Multiboot2. This keeps its fixed load span above the low-memory ACPI NVS and
SMM communication reservations exposed by Secure Boot OVMF.
- Workspace: single Cargo workspace so Global LTO spans everything.

## 4. Invariants & safety properties
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2 changes: 1 addition & 1 deletion build/xtask/src/main.rs
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Expand Up @@ -9982,7 +9982,7 @@ interface_resolution: 1024x768
\x20 probes.\n\
\x20 -cpu max is required: the kernel uses RDTSCP / RDSEED / etc. that the\n\
\x20 default qemu64 model doesn't expose.\n\
\x20 -m 1024M leaves room for the kernel image (~52 MiB at LOAD_BASE 16 MiB)\n\
\x20 -m 1024M leaves room for the kernel image (~52 MiB at LOAD_BASE 32 MiB)\n\
\x20 + UEFI's reservations + the 32 MiB static heap arena."
);
Ok(())
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