From 9592eef7c16ec5fb9f36c4d9abe8eeffc2e1d2f3 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Tue, 5 Jul 2022 20:48:41 +0200 Subject: random: remove CONFIG_ARCH_RANDOM When RDRAND was introduced, there was much discussion on whether it should be trusted and how the kernel should handle that. Initially, two mechanisms cropped up, CONFIG_ARCH_RANDOM, a compile time switch, and "nordrand", a boot-time switch. Later the thinking evolved. With a properly designed RNG, using RDRAND values alone won't harm anything, even if the outputs are malicious. Rather, the issue is whether those values are being *trusted* to be good or not. And so a new set of options were introduced as the real ones that people use -- CONFIG_RANDOM_TRUST_CPU and "random.trust_cpu". With these options, RDRAND is used, but it's not always credited. So in the worst case, it does nothing, and in the best case, maybe it helps. Along the way, CONFIG_ARCH_RANDOM's meaning got sort of pulled into the center and became something certain platforms force-select. The old options don't really help with much, and it's a bit odd to have special handling for these instructions when the kernel can deal fine with the existence or untrusted existence or broken existence or non-existence of that CPU capability. Simplify the situation by removing CONFIG_ARCH_RANDOM and using the ordinary asm-generic fallback pattern instead, keeping the two options that are actually used. For now it leaves "nordrand" for now, as the removal of that will take a different route. Acked-by: Michael Ellerman Acked-by: Catalin Marinas Acked-by: Borislav Petkov Acked-by: Heiko Carstens Acked-by: Greg Kroah-Hartman Signed-off-by: Jason A. Donenfeld --- arch/arm64/kernel/cpufeature.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'arch/arm64/kernel') diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 8d88433de81d..0e9462abeb77 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -2416,7 +2416,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .cpu_enable = cpu_enable_e0pd, }, #endif -#ifdef CONFIG_ARCH_RANDOM { .desc = "Random Number Generator", .capability = ARM64_HAS_RNG, @@ -2428,7 +2427,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .sign = FTR_UNSIGNED, .min_field_value = 1, }, -#endif #ifdef CONFIG_ARM64_BTI { .desc = "Branch Target Identification", -- cgit v1.2.3