Messages in this thread | | | Date | Thu, 23 Jun 2022 18:27:31 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: cpufeature: make sure cpu_mitigations_off then kpti off |
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On Thu, Jun 16, 2022 at 08:35:38PM +0800, Liu Song wrote: > From: Liu Song <liusong@linux.alibaba.com> > > If kaslr is enabled, kpti cannot be turned off even if "mitigations=off", > adjust the code order to ensure that kpti is off when "mitigations=off". > > Signed-off-by: Liu Song <liusong@linux.alibaba.com> > --- > arch/arm64/kernel/cpufeature.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 42ea2bd..27d4850 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1616,6 +1616,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > __kpti_forced = -1; > } > > + if (cpu_mitigations_off() && !__kpti_forced) { > + str = "mitigations=off"; > + __kpti_forced = -1; > + } > + > /* Useful for KASLR robustness */ > if (kaslr_requires_kpti()) { > if (!__kpti_forced) { > @@ -1624,11 +1629,6 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > } > } > > - if (cpu_mitigations_off() && !__kpti_forced) { > - str = "mitigations=off"; > - __kpti_forced = -1; > - }
The current behaviour is intentional: KASLR is trivial to bypass when kpti is disabled.
Will
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