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vmm: add compile-time validation for userfaultfd ioctl constants

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Cross-check each UFFDIO_* constant against the Linux _IOC(dir, type,
nr, size) encoding formula at compile time so that transposed direction
bits or struct sizes are caught immediately rather than silently
producing wrong ioctl numbers at runtime.

Signed-off-by: Shayon Mukherjee <shayonj@gmail.com>
This commit is contained in:
Shayon Mukherjee
2026-04-14 06:58:59 -04:00
committed by Rob Bradford
parent 72fc0976f1
commit 0a32a9ca91
1 changed files with 12 additions and 0 deletions
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12
vmm/src/userfaultfd.rs
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@@ -8,6 +8,18 @@ pub const UFFDIO_REGISTER: u64 = 0xc020_aa00; // _IOWR(0xAA, 0x00, struct uffdio
pub const UFFDIO_COPY: u64 = 0xc028_aa03; // _IOWR(0xAA, 0x03, struct uffdio_copy)
pub const UFFDIO_WAKE: u64 = 0x8010_aa02; // _IOR(0xAA, 0x02, struct uffdio_range)
// Validate ioctl encoding against the _IO{R,W,WR}(type, nr, size) formula so
// transposed direction bits or sizes are caught at compile time.
const fn ioctl_ioc(dir: u64, typ: u64, nr: u64, size: u64) -> u64 {
(dir << 30) | (size << 16) | (typ << 8) | nr
}
const IOC_READ: u64 = 2;
const IOC_READWRITE: u64 = 3;
const _: () = assert!(UFFDIO_API == ioctl_ioc(IOC_READWRITE, 0xAA, 0x3F, 24));
const _: () = assert!(UFFDIO_REGISTER == ioctl_ioc(IOC_READWRITE, 0xAA, 0x00, 32));
const _: () = assert!(UFFDIO_COPY == ioctl_ioc(IOC_READWRITE, 0xAA, 0x03, 40));
const _: () = assert!(UFFDIO_WAKE == ioctl_ioc(IOC_READ, 0xAA, 0x02, 16));
// Seccomp compares these as Dword (u32); ensure they fit.
const _: () = assert!(UFFDIO_API <= u32::MAX as u64);
const _: () = assert!(UFFDIO_REGISTER <= u32::MAX as u64);