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linux_rustix opt-in backend with linux_raw
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,125 @@ | ||
| //! Implementation for Linux / Android without `/dev/urandom` fallback | ||
| use crate::{Error, MaybeUninit}; | ||
| // use rustix::rand::{getrandom_uninit, GetRandomFlags}; | ||
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| pub use crate::util::{inner_u32, inner_u64}; | ||
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| #[cfg(not(any(target_os = "android", target_os = "linux")))] | ||
| compile_error!("`linux_raw` backend can be enabled only for Linux/Android targets!"); | ||
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| #[allow(non_upper_case_globals)] | ||
| unsafe fn getrandom_syscall(buf: *mut u8, buflen: usize, flags: u32) -> isize { | ||
| let r0; | ||
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| // Based on `rustix` and `linux-raw-sys` code. | ||
| cfg_if! { | ||
| if #[cfg(target_arch = "arm")] { | ||
| // In thumb-mode, r7 is the frame pointer and is not permitted to be used in | ||
| // an inline asm operand, so we have to use a different register and copy it | ||
| // into r7 inside the inline asm. | ||
| // Theoretically, we could detect thumb mode in the build script, but several | ||
| // register moves are cheap enough compared to the syscall cost, so we do not | ||
| // bother with it. | ||
| core::arch::asm!( | ||
| "mov {tmp}, r7", | ||
| "mov r7, #384", // __NR_getrandom = 384 | ||
| "svc 0", | ||
| "mov r7, {tmp}", | ||
| tmp = out(reg) _, | ||
| inlateout("r0") buf => r0, | ||
| in("r1") buflen, | ||
| in("r2") flags, | ||
| options(nostack, preserves_flags) | ||
| ); | ||
| } else if #[cfg(target_arch = "aarch64")] { | ||
| const __NR_getrandom: u32 = 278; | ||
| core::arch::asm!( | ||
| "svc 0", | ||
| in("x8") __NR_getrandom, | ||
| inlateout("x0") buf => r0, | ||
| in("x1") buflen, | ||
| in("x2") flags, | ||
| options(nostack, preserves_flags) | ||
| ); | ||
| } else if #[cfg(target_arch = "loongarch64")] { | ||
| const __NR_getrandom: u32 = 278; | ||
| core::arch::asm!( | ||
| "syscall 0", | ||
| in("$a7") __NR_getrandom, | ||
| inlateout("$a0") buf => r0, | ||
| in("$a1") buflen, | ||
| in("$a2") flags, | ||
| options(nostack, preserves_flags) | ||
| ); | ||
| } else if #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))] { | ||
| const __NR_getrandom: u32 = 278; | ||
| core::arch::asm!( | ||
| "ecall", | ||
| in("a7") __NR_getrandom, | ||
| inlateout("a0") buf => r0, | ||
| in("a1") buflen, | ||
| in("a2") flags, | ||
| options(nostack, preserves_flags) | ||
| ); | ||
| } else if #[cfg(target_arch = "x86")] { | ||
| const __NR_getrandom: isize = 355; | ||
| // `int 0x80` is famously slow, but implementing vDSO is too complex | ||
| // and `sysenter`/`syscall` have their own portability issues, | ||
| // so we use the simple "legacy" way of doing syscalls. | ||
| core::arch::asm!( | ||
| "int $$0x80", | ||
| inlateout("eax") __NR_getrandom => r0, | ||
| in("ebx") buf, | ||
| in("ecx") buflen, | ||
| in("edx") flags, | ||
| options(nostack, preserves_flags) | ||
| ); | ||
| } else if #[cfg(target_arch = "x86_64")] { | ||
| #[cfg(target_pointer_width = "64")] | ||
| const __NR_getrandom: isize = 318; | ||
| #[cfg(target_pointer_width = "32")] | ||
| const __NR_getrandom: isize = 1073742142; | ||
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| core::arch::asm!( | ||
| "syscall", | ||
| inlateout("rax") __NR_getrandom => r0, | ||
| in("rdi") buf, | ||
| in("rsi") buflen, | ||
| in("rdx") flags, | ||
| lateout("rcx") _, | ||
| lateout("r11") _, | ||
| options(nostack, preserves_flags) | ||
| ); | ||
| } else { | ||
| compile_error!("`linux_raw` backend does not support this target arch"); | ||
| } | ||
| } | ||
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| r0 | ||
| } | ||
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| pub fn fill_inner(mut dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> { | ||
| // Value of this error code is stable across all target arches. | ||
| const EINTR: isize = -4; | ||
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| loop { | ||
| let ret = unsafe { getrandom_syscall(dest.as_mut_ptr().cast(), dest.len(), 0) }; | ||
| match usize::try_from(ret) { | ||
| Ok(0) => return Err(Error::UNEXPECTED), | ||
| Ok(len) => { | ||
| dest = dest.get_mut(len..).ok_or(Error::UNEXPECTED)?; | ||
| if dest.is_empty() { | ||
| return Ok(()); | ||
| } | ||
| } | ||
| Err(_) if ret == EINTR => continue, | ||
| Err(_) => { | ||
| let code: u32 = ret | ||
| .wrapping_neg() | ||
| .try_into() | ||
| .map_err(|_| Error::UNEXPECTED)?; | ||
| return Err(Error::from_os_error(code)); | ||
| } | ||
| } | ||
| } | ||
| } |
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