arm64: set UXN on swapper page tables

BugLink: https://bugs.launchpad.net/bugs/1989221
[ This issue was fixed upstream by accident in c3cee924bd85 ("arm64:
  head: cover entire kernel image in initial ID map") as part of a
  large refactoring of the arm64 boot flow. This simple fix is therefore
  preferred for -stable backporting ]

On a system that implements FEAT_EPAN, read/write access to the idmap
is denied because UXN is not set on the swapper PTEs. As a result,
idmap_kpti_install_ng_mappings panics the kernel when accessing
__idmap_kpti_flag. Fix it by setting UXN on these PTEs.

Fixes: 18107f8a2df6 ("arm64: Support execute-only permissions with Enhanced PAN")
Cc: <stable@vger.kernel.org> # 5.15
Link: https://linux-review.googlesource.com/id/Ic452fa4b4f74753e54f71e61027e7222a0fae1b1
Signed-off-by: Peter Collingbourne <pcc@google.com>
Acked-by: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220719234909.1398992-1-pcc@google.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index 96dc0f7da258d9628a2e5a06557e3376f4089bd4..a971d462f531c0172669c0ce0bd6817f375c2633 100644 (file)
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -103,8 +103,8 @@
 /*
  * Initial memory map attributes.
  */
-#define SWAPPER_PTE_FLAGS      (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
-#define SWAPPER_PMD_FLAGS      (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)
+#define SWAPPER_PTE_FLAGS      (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED | PTE_UXN)
+#define SWAPPER_PMD_FLAGS      (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S | PMD_SECT_UXN)
 
 #if ARM64_KERNEL_USES_PMD_MAPS
 #define SWAPPER_MM_MMUFLAGS    (PMD_ATTRINDX(MT_NORMAL) | SWAPPER_PMD_FLAGS)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 17962452e31de6a04d1c0d3cc924142478e1a4b3..ab6566bf1c3321e08188980562fabacd1f094b1d 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -285,7 +285,7 @@ SYM_FUNC_START_LOCAL(__create_page_tables)
        subs    x1, x1, #64
        b.ne    1b
 
-       mov     x7, SWAPPER_MM_MMUFLAGS
+       mov_q   x7, SWAPPER_MM_MMUFLAGS
 
        /*
         * Create the identity mapping.