From: Mark Brown <broonie@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>, linux-arm-kernel@lists.infradead.org
Subject: [PATCH 2/2] arm64: Don't use KPTI where we have E0PD
Date: Mon, 12 Aug 2019 13:57:38 +0100 [thread overview]
Message-ID: <20190812125738.17388-3-broonie@kernel.org> (raw)
In-Reply-To: <20190812125738.17388-1-broonie@kernel.org>
Since E0PD is intended to fulfil the same role as KPTI we don't need to
use KPTI on CPUs where E0PD is available, we can rely on E0PD instead.
Change the check that forces KPTI on when KASLR is enabled to check for
E0PD before doing so, CPUs with E0PD are not expected to be affected by
meltdown so should not need to enable KPTI for other reasons.
Since we repeat the KPTI check for all CPUs we will still enable KPTI if
any of the CPUs in the system lacks E0PD. Since KPTI itself is not changed
by this patch once we enable KPTI we will do so for all CPUs. This is safe
but not optimally performant for such systems.
KPTI can still be forced on from the command line if required.
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/kernel/cpufeature.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 4aa1d2026bef..322004409211 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -995,7 +995,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
/* Useful for KASLR robustness */
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_offset() > 0) {
- if (!__kpti_forced) {
+ if (!__kpti_forced && !this_cpu_has_cap(ARM64_HAS_E0PD)) {
str = "KASLR";
__kpti_forced = 1;
}
--
2.20.1
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next prev parent reply other threads:[~2019-08-12 12:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 12:57 [0/2] arm64: E0PD support Mark Brown
2019-08-12 12:57 ` [PATCH 1/2] arm64: Add initial support for E0PD Mark Brown
2019-08-13 9:59 ` Suzuki K Poulose
2019-08-13 17:25 ` Will Deacon
2019-08-12 12:57 ` Mark Brown [this message]
2019-08-13 10:01 ` [PATCH 2/2] arm64: Don't use KPTI where we have E0PD Suzuki K Poulose
2019-08-13 17:28 ` Will Deacon
2019-08-13 19:05 ` Mark Brown
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