arm64: bti: Fix support for userspace only BTI

When setting PTE_MAYBE_GP we check system_supports_bti() but this is
true for systems where only CONFIG_BTI is set causing us to enable BTI
on some kernel text. Add an extra check for the kernel mode option,
using an ifdef due to line length.

Fixes: c8027285e366 ("arm64: Set GP bit in kernel page tables to enable BTI for the kernel")
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20200512113950.29996-1-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 3106903..2e7e0f4 100644 (file)
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -32,7 +32,15 @@ extern bool arm64_use_ng_mappings;
 #define PTE_MAYBE_NG           (arm64_use_ng_mappings ? PTE_NG : 0)
 #define PMD_MAYBE_NG           (arm64_use_ng_mappings ? PMD_SECT_NG : 0)
 
+/*
+ * If we have userspace only BTI we don't want to mark kernel pages
+ * guarded even if the system does support BTI.
+ */
+#ifdef CONFIG_ARM64_BTI_KERNEL
 #define PTE_MAYBE_GP           (system_supports_bti() ? PTE_GP : 0)
+#else
+#define PTE_MAYBE_GP           0
+#endif
 
 #define PROT_DEFAULT           (_PROT_DEFAULT | PTE_MAYBE_NG)
 #define PROT_SECT_DEFAULT      (_PROT_SECT_DEFAULT | PMD_MAYBE_NG)