From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Pedro Falcato <pedro.falcato@gmail.com>
Cc: devel@edk2.groups.io, ardb@kernel.org,
Liming Gao <gaoliming@byosoft.com.cn>,
Rebecca Cran <rebecca@bsdio.com>,
Pierre Gondois <pierre.gondois@arm.com>,
Leif Lindholm <quic_llindhol@quicinc.com>,
Sami Mujawar <sami.mujawar@arm.com>,
Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: [edk2-devel] [PATCH 3/3] OvmfPkg/OvmfX86: Enable RDRAND based EFI_RNG_PROTOCOL implementation
Date: Tue, 22 Nov 2022 13:29:55 +0100 [thread overview]
Message-ID: <Y3zAw3pHZ430OKF+@zx2c4.com> (raw)
In-Reply-To: <CAKbZUD30=NA-7uD-qQvLC0r4cYrDJStsB47q_MyLf75kh67cKw@mail.gmail.com>
Hi again,
On Tue, Nov 22, 2022 at 11:35:06AM +0000, Pedro Falcato wrote:
> We should probably also test for stupidly broken rdrand implementations
> like the notorious Zen 3 which always return 0xFFFFFFFF (per xkcd 221 ;)).
On this topic, if you did want to improve this part of that DXE, the
kernel's test for this is super dumb and basic but I think basically
gets the job done for the most pathological scenarios.
>From arch/x86/kernel/cpu/rdrand.c:
void x86_init_rdrand(struct cpuinfo_x86 *c)
{
enum { SAMPLES = 8, MIN_CHANGE = 5 };
unsigned long sample, prev;
bool failure = false;
size_t i, changed;
if (!cpu_has(c, X86_FEATURE_RDRAND))
return;
for (changed = 0, i = 0; i < SAMPLES; ++i) {
if (!rdrand_long(&sample)) {
failure = true;
break;
}
changed += i && sample != prev;
prev = sample;
}
if (changed < MIN_CHANGE)
failure = true;
if (failure) {
clear_cpu_cap(c, X86_FEATURE_RDRAND);
clear_cpu_cap(c, X86_FEATURE_RDSEED);
pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
}
}
Feel free to lift that into the DXE if you want. That should probably be
a different patch to this series, though, as I mentioned in my last
email. The CPUID check that you mentioned, however, seems like an
important prerequisite to this series.
Jason
next prev parent reply other threads:[~2022-11-22 12:30 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-10 13:47 [PATCH 0/3] OVMF: support EFI_RNG_PROTOCOL without virtio-rng Ard Biesheuvel
2022-11-10 13:47 ` [PATCH 1/3] ArmPkg/ArmTrngLib: Fix incorrect GUID reference in DEBUG() output Ard Biesheuvel
2022-11-10 14:39 ` Sami Mujawar
2022-11-10 13:47 ` [PATCH 2/3] ArmVirtPkg/ArmVirtQemu: Expose TRNG hypercall via RngDxe if implemented Ard Biesheuvel
2022-11-18 16:48 ` PierreGondois
2023-01-11 16:49 ` [edk2-devel] " Ard Biesheuvel
2023-01-11 17:38 ` PierreGondois
2023-01-11 17:45 ` Ard Biesheuvel
2022-11-10 13:47 ` [PATCH 3/3] OvmfPkg/OvmfX86: Enable RDRAND based EFI_RNG_PROTOCOL implementation Ard Biesheuvel
2022-11-22 11:35 ` [edk2-devel] " Pedro Falcato
2022-11-22 12:20 ` Jason A. Donenfeld
2022-11-22 12:45 ` Pedro Falcato
2022-11-22 13:10 ` Jason A. Donenfeld
2022-11-22 14:17 ` Pedro Falcato
2022-11-22 14:21 ` Jason A. Donenfeld
2022-11-22 12:29 ` Jason A. Donenfeld [this message]
2022-11-11 0:41 ` 回复: [PATCH 0/3] OVMF: support EFI_RNG_PROTOCOL without virtio-rng gaoliming
2022-11-11 2:41 ` Jason A. Donenfeld
2022-11-11 7:47 ` Ard Biesheuvel
2022-11-11 17:03 ` Jason A. Donenfeld
[not found] ` <172660F4A69E435E.25609@groups.io>
2022-11-11 3:53 ` 回复: [edk2-devel] 回复: " gaoliming
2022-11-11 7:34 ` Ard Biesheuvel
2022-11-11 8:14 ` [edk2-devel] " Gerd Hoffmann
2023-01-10 18:19 ` Jason A. Donenfeld
2023-01-11 11:41 ` Ard Biesheuvel
2023-01-11 15:23 ` [edk2-devel] " Laszlo Ersek
2023-01-11 16:03 ` Ard Biesheuvel
2023-01-11 16:05 ` Ard Biesheuvel
2023-01-12 9:27 ` Laszlo Ersek
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