Messages in this thread | | | Date | Mon, 30 Mar 2020 15:14:30 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] random: Drop ARCH limitations for CONFIG_RANDOM_TRUST_CPU |
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On Sun, Mar 29, 2020 at 12:56:24PM -0400, Theodore Y. Ts'o wrote: > On Sun, Mar 29, 2020 at 10:29:09AM +0200, Alexander Sverdlin wrote: > > The option itself looks attractive for the embedded devices which often > > have HWRNG but less entropy from user-input. And these devices are often > > ARM/ARM64 or MIPS. The reason to limit it to X86/S390/PPC is not obvious. > > > > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com> > > This feature is *only* applicable if the CPU supports a > arch_get_random_seed_long() or arch_get_random_long(). I believe > there are some server-class ARM64 CPU's that support such an > instruction, but I don't believe any of the embedded arm64 --- and > certainly non of the embedded arm --- SOC's support > arch_get_random_long(). > > The reason why we limited it to X86/S390/PPC is because those were the > platforms which supported an RDRAND-like instruction at the time. > Richard Henderson added support for ARM64 in commit 1a50ec0b3b2e > ("arm64: Implement archrandom.h for ARMv8.5-RNG") in late January 2020. > > So we should either add ARM64 to the dependency list, or we could, as > you suggest, simply remove the dependency altogether. The tradeoff is > that it will cause an extra CONFIG prompt on a number of platforms > (mips, arm, sparc, etc.) where it will be utterly pointless since > those architectures have no chance of support a RDRAND-like > instruction.
Just for anyone watching, the dependency rework is already handled in linux-next by commit:
23ae0c17b89cfeb5 ("random: Make RANDOM_TRUST_CPU depend on ARCH_RANDOM")
... where x86, s390, ppc, and arm64 all select ARCH_RANDOM.
Mark.
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