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Reduce duplication in is_available #17

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Apr 15, 2022
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Reduce duplication in is_available #17

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73 changes: 46 additions & 27 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -158,43 +158,62 @@ macro_rules! loop_rand {
}};
}

// NB: On AMD processor families < 0x17, we want to unconditionally disable RDRAND
// and RDSEED. Executing these instructions on these processors can return
// non-random data (0) while also reporting a success.
//
// See:
// * https://github.com/systemd/systemd/issues/11810
// * https://lore.kernel.org/all/776cb5c2d33e7fd0d2893904724c0e52b394f24a.1565817448.git.thomas.lendacky@amd.com/
//
// We take extra care to do so even if `-Ctarget-features=+rdrand` have been
// specified, in order to prevent users from shooting themselves in their feet.
#[inline(always)]
fn authentic_amd() -> bool {
let cpuid0 = unsafe { arch::__cpuid(0) };
matches!(
(cpuid0.ebx, cpuid0.ecx, cpuid0.edx),
(0x68747541, 0x444D4163, 0x69746E65)
)
}

#[inline(always)]
fn amd_family(cpuid1: &arch::CpuidResult) -> u32 {
((cpuid1.eax >> 8) & 0xF) + ((cpuid1.eax >> 20) & 0xFF)
}

#[inline(always)]
fn has_rdrand(cpuid1: &arch::CpuidResult) -> bool {
const FLAG: u32 = 1 << 30;
cpuid1.ecx & FLAG == FLAG
}

#[inline(always)]
fn has_rdseed() -> bool {
const FLAG: u32 = 1 << 18;
unsafe { arch::__cpuid(7).ebx & FLAG == FLAG }
}

/// NB: On AMD processor families < 0x17, we want to unconditionally disable RDRAND
/// and RDSEED. Executing these instructions on these processors can return
/// non-random data (0) while also reporting a success.
///
/// See:
/// * https://github.com/systemd/systemd/issues/11810
/// * https://lore.kernel.org/all/776cb5c2d33e7fd0d2893904724c0e52b394f24a.1565817448.git.thomas.lendacky@amd.com/
///
/// We take extra care to do so even if `-Ctarget-features=+rdrand` have been
/// specified, in order to prevent users from shooting themselves in their feet.
const FIRST_GOOD_AMD_FAMILY: u32 = 0x17;

macro_rules! is_available {
("rdrand") => {{
const FLAG: u32 = 1 << 30;
let cpuid0 = unsafe { arch::__cpuid(0) };
if let (0x68747541, 0x444D4163, 0x69746E65) = (cpuid0.ebx, cpuid0.ecx, cpuid0.edx) {
// This is an AuthenticAMD chip.
if authentic_amd() {
let cpuid1 = unsafe { arch::__cpuid(1) };
let family = ((cpuid1.eax >> 8) & 0xF) + ((cpuid1.eax >> 20) & 0xFF);
(cpuid1.ecx & FLAG == FLAG) && (family >= 0x17)
has_rdrand(&cpuid1) && (amd_family(&cpuid1) >= FIRST_GOOD_AMD_FAMILY)
} else {
cfg!(target_feature="rdrand") || unsafe { arch::__cpuid(1).ecx & FLAG == FLAG }
cfg!(target_feature = "rdrand") || has_rdrand(&unsafe { arch::__cpuid(1) })
}
}};
("rdseed") => {{
const FLAG : u32 = 1 << 18;
let cpuid0 = unsafe { arch::__cpuid(0) };
if let (0x68747541, 0x444D4163, 0x69746E65) = (cpuid0.ebx, cpuid0.ecx, cpuid0.edx) {
let cpuid1 = unsafe { arch::__cpuid(1) };
let family = ((cpuid1.eax >> 8) & 0xF) + ((cpuid1.eax >> 20) & 0xFF);
(family >= 0x17) && unsafe { arch::__cpuid(7).ebx & FLAG == FLAG }
if authentic_amd() {
(amd_family(&unsafe { arch::__cpuid(1) }) >= FIRST_GOOD_AMD_FAMILY) && has_rdseed()
} else {
cfg!(target_feature="rdrand") || unsafe { arch::__cpuid(7).ebx & FLAG == FLAG }
cfg!(target_feature = "rdrand") || has_rdseed()
}
}};
}


macro_rules! impl_rand {
($gen:ident, $feat:tt, $step16: path, $step32:path, $step64:path,
maxstep = $maxstep:path, maxty = $maxty: ty) => {
Expand All @@ -205,8 +224,8 @@ macro_rules! impl_rand {
/// instruction necessary for this generator to operate. If the instruction is not
/// supported, an error is returned.
pub fn new() -> Result<Self, ErrorCode> {
if cfg!(target_env="sgx") {
if cfg!(target_feature=$feat) {
if cfg!(target_env = "sgx") {
if cfg!(target_feature = $feat) {
Ok($gen(()))
} else {
Err(ErrorCode::UnsupportedInstruction)
Expand Down