Thread (48 messages) 48 messages, 3 authors, 2021-10-11

Re: [PATCH v6 04/22] powerpc/book3s64/kuap/kuep: Move uamor setup to pkey init

From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2020-11-26 03:29:46

"Aneesh Kumar K.V" [off-list ref] writes:
quoted hunk ↗ jump to hunk
This patch consolidates UAMOR update across pkey, kuap and kuep features.
The boot cpu initialize UAMOR via pkey init and both radix/hash do the
secondary cpu UAMOR init in early_init_mmu_secondary.

We don't check for mmu_feature in radix secondary init because UAMOR
is a supported SPRN with all CPUs supporting radix translation.
The old code was not updating UAMOR if we had smap disabled and smep enabled.
This change handles that case.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/mm/book3s64/radix_pgtable.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index 3adcf730f478..bfe441af916a 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -620,9 +620,6 @@ void setup_kuap(bool disabled)
 		cur_cpu_spec->mmu_features |= MMU_FTR_RADIX_KUAP;
 	}
 
-	/* Make sure userspace can't change the AMR */
-	mtspr(SPRN_UAMOR, 0);
-
 	/*
 	 * Set the default kernel AMR values on all cpus.
 	 */
@@ -721,6 +718,11 @@ void radix__early_init_mmu_secondary(void)
 
 	radix__switch_mmu_context(NULL, &init_mm);
 	tlbiel_all();
+
+#ifdef CONFIG_PPC_PKEY
+	/* Make sure userspace can't change the AMR */
+	mtspr(SPRN_UAMOR, 0);
+#endif
If PPC_PKEY is disabled I think this leaves UAMOR unset, which means it
could potentially allow AMR to be used as a covert channel between
processes.

cheers
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