linux-bzimage-builder 0.17.1

// SPDX-License-Identifier: MPL-2.0

//! Big zImage PE/COFF header generation.
//!
//! The definition of the PE/COFF header is in the Microsoft PE/COFF specification:
//! <https://learn.microsoft.com/en-us/windows/win32/debug/pe-format>
//!
//! The reference to the Linux PE header definition:
//! <https://github.com/torvalds/linux/blob/master/include/linux/pe.h>

use std::vec;

use align_ext::AlignExt;
use serde::Serialize;
use zerocopy::IntoBytes;

use crate::mapping::{LEGACY_SETUP_SEC_SIZE, SetupFileOffset, SetupVA};

// The MS-DOS header.
const MZ_MAGIC: u16 = 0x5a4d; // "MZ"

// The `magic` field in PE header.
const PE_MAGIC: u32 = 0x00004550;

// The `machine` field choices in PE header. Not exhaustive.
#[derive(Serialize, Clone, Copy)]
#[repr(u16)]
enum PeMachineType {
    Amd64 = 0x8664,
}

// The `flags` field choices in PE header.
bitflags::bitflags! {
    struct PeFlags: u16 {
        const RELOCS_STRIPPED           = 1;
        const EXECUTABLE_IMAGE          = 1 << 1;
        const LINE_NUMS_STRIPPED        = 1 << 2;
        const LOCAL_SYMS_STRIPPED       = 1 << 3;
        const AGGRESSIVE_WS_TRIM         = 1 << 4;
        const LARGE_ADDRESS_AWARE       = 1 << 5;
        const SIXTEEN_BIT_MACHINE       = 1 << 6;
        const BYTES_REVERSED_LO         = 1 << 7;
        const THIRTY_TWO_BIT_MACHINE    = 1 << 8;
        const DEBUG_STRIPPED            = 1 << 9;
        const REMOVABLE_RUN_FROM_SWAP   = 1 << 10;
        const NET_RUN_FROM_SWAP         = 1 << 11;
        const SYSTEM                    = 1 << 12;
        const DLL                       = 1 << 13;
        const UP_SYSTEM_ONLY            = 1 << 14;
    }
}

#[derive(Pod, Serialize, Clone, Copy)]
#[repr(C, packed)]
struct PeHdr {
    magic: u32,        // PE magic
    machine: u16,      // machine type
    sections: u16,     // number of sections
    timestamp: u32,    // time_t
    symbol_table: u32, // symbol table offset
    symbols: u32,      // number of symbols
    opt_hdr_size: u16, // size of optional header
    flags: u16,        // flags
}

// The `magic` field in the PE32+ optional header.
const PE32PLUS_OPT_HDR_MAGIC: u16 = 0x020b;

// The `subsys` field choices in the PE32+ optional header. Not exhaustive.
#[derive(Serialize, Clone, Copy)]
#[repr(u16)]
enum PeImageSubsystem {
    EfiApplication = 10,
}

#[derive(Pod, Serialize, Clone, Copy)]
#[repr(C, packed)]
struct Pe32PlusOptHdr {
    magic: u16,          // file type
    ld_major: u8,        // linker major version
    ld_minor: u8,        // linker minor version
    text_size: u32,      // size of text section(s)
    data_size: u32,      // size of data section(s)
    bss_size: u32,       // size of bss section(s)
    entry_point: u32,    // file offset of entry point
    code_base: u32,      // relative code addr in ram
    image_base: u64,     // preferred load address
    section_align: u32,  // alignment in bytes
    file_align: u32,     // file alignment in bytes
    os_major: u16,       // major OS version
    os_minor: u16,       // minor OS version
    image_major: u16,    // major image version
    image_minor: u16,    // minor image version
    subsys_major: u16,   // major subsystem version
    subsys_minor: u16,   // minor subsystem version
    win32_version: u32,  // reserved, must be 0
    image_size: u32,     // image size
    header_size: u32,    // header size rounded up to file_align
    csum: u32,           // checksum
    subsys: u16,         // subsystem
    dll_flags: u16,      // more flags!
    stack_size_req: u64, // amt of stack requested
    stack_size: u64,     // amt of stack required
    heap_size_req: u64,  // amt of heap requested
    heap_size: u64,      // amt of heap required
    loader_flags: u32,   // reserved, must be 0
    data_dirs: u32,      // number of data dir entries
}

#[derive(Pod, Serialize, Clone, Copy)]
#[repr(C, packed)]
struct Pe32PlusOptDataDirEnt {
    /// The RVA is the address of the table relative to the base address of the image when the table is loaded.
    rva: u32,
    size: u32,
}

impl Pe32PlusOptDataDirEnt {
    fn none() -> Self {
        Self { rva: 0, size: 0 }
    }
}

/// The data directories in the PE32+ optional header.
///
/// The `data_dirs` number field in the PE32+ optional header is just an illusion that you can choose to have a
/// subset of the data directories. The actual number of data directories is fixed to 16 and you can only ignore
/// data directories at the end of the list. We ignore data directories after the 8th as what Linux do.
#[derive(Pod, Serialize, Clone, Copy)]
#[repr(C, packed)]
struct Pe32PlusOptDataDirs {
    export_table: Pe32PlusOptDataDirEnt,
    import_table: Pe32PlusOptDataDirEnt,
    resource_table: Pe32PlusOptDataDirEnt,
    exception_table: Pe32PlusOptDataDirEnt,
    certificate_table: Pe32PlusOptDataDirEnt,
    base_relocation_table: Pe32PlusOptDataDirEnt,
}

impl Pe32PlusOptDataDirs {
    fn num_dirs() -> usize {
        size_of::<Self>() / size_of::<Pe32PlusOptDataDirEnt>()
    }
}

// The `flags` field choices in the PE section header.
// Excluding the alignment flags, which is not bitflags.
bitflags::bitflags! {
    struct PeSectionHdrFlags: u32 {
        const CNT_CODE                  = 1 << 5;
        const CNT_INITIALIZED_DATA      = 1 << 6;
        const CNT_UNINITIALIZED_DATA    = 1 << 7;
        const LNK_INFO                  = 1 << 9;
        const LNK_REMOVE                = 1 << 11;
        const LNK_COMDAT                = 1 << 12;
        const GPREL	                    = 1 << 15;
        const MEM_PURGEABLE             = 1 << 16;
        const LNK_NRELOC_OVFL           = 1 << 24;
        const MEM_DISCARDABLE           = 1 << 25;
        const MEM_NOT_CACHED            = 1 << 26;
        const MEM_NOT_PAGED             = 1 << 27;
        const MEM_SHARED                = 1 << 28;
        const MEM_EXECUTE               = 1 << 29;
        const MEM_READ                  = 1 << 30;
        const MEM_WRITE                 = 1 << 31;
    }
}

#[derive(Pod, Serialize, Clone, Copy)]
#[repr(C, packed)]
struct PeSectionHdr {
    name: [u8; 8],        // name or "/12\0" string tbl offset
    virtual_size: u32,    // size of loaded section in RAM
    virtual_address: u32, // relative virtual address
    raw_data_size: u32,   // size of the section
    data_addr: u32,       // file pointer to first page of sec
    relocs: u32,          // file pointer to relocation entries
    line_numbers: u32,    // line numbers!
    num_relocs: u16,      // number of relocations
    num_lin_numbers: u16, // srsly.
    flags: u32,
}

pub(super) const SECTION_ALIGNMENT: usize = 4096;
const FILE_ALIGNMENT: usize = 512;

pub(crate) fn make_pe_coff_header(setup_elf: &[u8]) -> Vec<u8> {
    let elf = xmas_elf::ElfFile::new(setup_elf).unwrap();
    let mut bin = Vec::<u8>::new();

    // PE header
    let mut pe_hdr = PeHdr {
        magic: PE_MAGIC,
        machine: PeMachineType::Amd64 as u16,
        sections: 0, // this field will be modified later
        timestamp: 0,
        symbol_table: 0,
        symbols: 1, // I don't know why, Linux header.S says it's 1
        opt_hdr_size: (size_of::<Pe32PlusOptHdr>() + size_of::<Pe32PlusOptDataDirs>()) as u16,
        flags: (PeFlags::EXECUTABLE_IMAGE | PeFlags::DEBUG_STRIPPED | PeFlags::LINE_NUMS_STRIPPED)
            .bits,
    };

    let sec_hdrs = build_pe_sec_headers_from(&elf);

    // PE32+ optional header
    let pe_opt_hdr = Pe32PlusOptHdr {
        magic: PE32PLUS_OPT_HDR_MAGIC,
        ld_major: 0x02, // there's no linker to this extent, we do linking by ourselves
        ld_minor: 0x14,
        text_size: sec_hdrs.text.raw_data_size,
        data_size: sec_hdrs.rodata.raw_data_size + sec_hdrs.data.raw_data_size,
        bss_size: 0, // bss size is irrelevant
        entry_point: (elf.header.pt2.entry_point() - sec_hdrs.base as u64) as u32,
        code_base: sec_hdrs.text.virtual_address,
        image_base: 0,
        section_align: SECTION_ALIGNMENT as u32,
        file_align: FILE_ALIGNMENT as u32,
        os_major: 0,
        os_minor: 0,
        image_major: 0x3, // see linux/pe.h for more info
        image_minor: 0,
        subsys_major: 0,
        subsys_minor: 0,
        win32_version: 0,
        image_size: sec_hdrs.data.virtual_address + sec_hdrs.data.virtual_size,
        header_size: LEGACY_SETUP_SEC_SIZE as u32,
        csum: 0,
        subsys: PeImageSubsystem::EfiApplication as u16,
        dll_flags: 0x100, // NX compatible
        stack_size_req: 0,
        stack_size: 0,
        heap_size_req: 0,
        heap_size: 0,
        loader_flags: 0,
        data_dirs: Pe32PlusOptDataDirs::num_dirs() as u32,
    };

    let pe_opt_hdr_data_dirs = Pe32PlusOptDataDirs {
        export_table: Pe32PlusOptDataDirEnt::none(),
        import_table: Pe32PlusOptDataDirEnt::none(),
        resource_table: Pe32PlusOptDataDirEnt::none(),
        exception_table: Pe32PlusOptDataDirEnt::none(),
        certificate_table: Pe32PlusOptDataDirEnt::none(),
        base_relocation_table: Pe32PlusOptDataDirEnt::none(),
    };

    // PE section headers
    let AllPeSectionHdrs {
        base: _,
        text,
        rodata,
        data,
    } = sec_hdrs;
    let sec_hdr_vec = vec![text, rodata, data];

    // Write the MS-DOS header
    bin.extend_from_slice(&MZ_MAGIC.to_le_bytes());
    // Write the MS-DOS stub at 0x3c
    bin.extend_from_slice(&[0x0; 0x3c - 0x2]);
    // Write the PE header offset, the header is right after the offset field
    bin.extend_from_slice(&(0x3cu32 + size_of::<u32>() as u32).to_le_bytes());

    // Write the PE header
    pe_hdr.sections = sec_hdr_vec.len() as u16;
    bin.extend_from_slice(pe_hdr.as_bytes());
    // Write the PE32+ optional header
    bin.extend_from_slice(pe_opt_hdr.as_bytes());
    bin.extend_from_slice(pe_opt_hdr_data_dirs.as_bytes());
    // Write the PE section headers
    for sec_hdr in sec_hdr_vec {
        bin.extend_from_slice(sec_hdr.as_bytes());
    }

    bin
}

impl PeSectionHdr {
    fn new_text(
        virtual_size: u32,
        virtual_address: u32,
        raw_data_size: u32,
        data_addr: u32,
    ) -> Self {
        Self {
            name: [b'.', b't', b'e', b'x', b't', 0, 0, 0],
            virtual_size,
            virtual_address,
            raw_data_size,
            data_addr,
            relocs: 0,
            line_numbers: 0,
            num_relocs: 0,
            num_lin_numbers: 0,
            flags: (PeSectionHdrFlags::CNT_CODE
                | PeSectionHdrFlags::MEM_READ
                | PeSectionHdrFlags::MEM_EXECUTE)
                .bits(),
        }
    }

    fn new_data(
        virtual_size: u32,
        virtual_address: u32,
        raw_data_size: u32,
        data_addr: u32,
    ) -> Self {
        Self {
            name: [b'.', b'd', b'a', b't', b'a', 0, 0, 0],
            virtual_size,
            virtual_address,
            raw_data_size,
            data_addr,
            relocs: 0,
            line_numbers: 0,
            num_relocs: 0,
            num_lin_numbers: 0,
            flags: (PeSectionHdrFlags::CNT_INITIALIZED_DATA
                | PeSectionHdrFlags::MEM_READ
                | PeSectionHdrFlags::MEM_WRITE)
                .bits(),
        }
    }

    fn new_rodata(
        virtual_size: u32,
        virtual_address: u32,
        raw_data_size: u32,
        data_addr: u32,
    ) -> Self {
        Self {
            name: [b'.', b'r', b'o', b'd', b'a', b't', b'a', 0],
            virtual_size,
            virtual_address,
            raw_data_size,
            data_addr,
            relocs: 0,
            line_numbers: 0,
            num_relocs: 0,
            num_lin_numbers: 0,
            flags: (PeSectionHdrFlags::CNT_INITIALIZED_DATA | PeSectionHdrFlags::MEM_READ).bits(),
        }
    }
}

struct AllPeSectionHdrs {
    /// The base for all virtual addresses in the PE/COFF header.
    ///
    /// We need this because we want to set `image_base` in `Pe32PlusOptHdr` to zero. Otherwise
    /// some UEFI firmware will refuse to load the image. (FIXME: This is what Linux does, but I
    /// can't find any specification that says we have to do this).
    base: usize,
    text: PeSectionHdr,
    rodata: PeSectionHdr,
    data: PeSectionHdr,
}

fn build_pe_sec_headers_from(elf: &xmas_elf::ElfFile) -> AllPeSectionHdrs {
    fn new_pe_sec_header(
        segment: &xmas_elf::program::ProgramHeader,
        base: usize,
        f: impl FnOnce(u32, u32, u32, u32) -> PeSectionHdr,
    ) -> PeSectionHdr {
        assert_eq!(
            segment.virtual_addr() as usize % SECTION_ALIGNMENT,
            0,
            "the segment virtual address must be aligned",
        );

        let va = SetupVA::from(segment.virtual_addr() as usize);
        let len = (segment.mem_size() as usize).align_up(SECTION_ALIGNMENT);

        f(
            len as u32,
            (usize::from(va) - base) as u32,
            len as u32,
            usize::from(SetupFileOffset::from(va)) as u32,
        )
    }

    let segments = elf.program_iter().collect::<Vec<_>>();

    // There should be four segments: "header", "text", "rodata", and "data".
    assert_eq!(segments.len(), 4, "there must be four segments");
    assert!(
        segments[1].flags().is_execute(),
        "the text segment must be executable",
    );
    assert!(
        segments[2].flags().is_read(),
        "the text segment must be readable",
    );
    assert!(
        segments[3].flags().is_write(),
        "the data segment must be writable",
    );

    // The "header" segment won't be loaded. See the linker script for details.

    let base = segments[1].virtual_addr() as usize - SECTION_ALIGNMENT;
    AllPeSectionHdrs {
        base,
        text: new_pe_sec_header(&segments[1], base, PeSectionHdr::new_text),
        rodata: new_pe_sec_header(&segments[2], base, PeSectionHdr::new_rodata),
        data: new_pe_sec_header(&segments[3], base, PeSectionHdr::new_data),
    }
}