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Subject[PATCH 4.7 003/143] x86/platform/uv: Skip UV runtime services mapping in the efi_runtime_disabled case
4.7-stable review patch.  If anyone has any objections, please let me know.


From: Alex Thorlton <>

commit f72075c9eda8a43aeea2f9dbb8d187afd4a76f0b upstream.

This problem has actually been in the UV code for a while, but we didn't
catch it until recently, because we had been relying on EFI_OLD_MEMMAP
to allow our systems to boot for a period of time. We noticed the issue
when trying to kexec a recent community kernel, where we hit this NULL
pointer dereference in efi_sync_low_kernel_mappings():

[ 0.337515] BUG: unable to handle kernel NULL pointer dereference at 0000000000000880
[ 0.346276] IP: [<ffffffff8105df8d>] efi_sync_low_kernel_mappings+0x5d/0x1b0

The problem doesn't show up with EFI_OLD_MEMMAP because we skip the
chunk of setup_efi_state() that sets the efi_loader_signature for the
kexec'd kernel. When the kexec'd kernel boots, it won't set EFI_BOOT in
setup_arch, so we completely avoid the bug.

We always kexec with noefi on the command line, so this shouldn't be an
issue, but since we're not actually checking for efi_runtime_disabled in
uv_bios_init(), we end up trying to do EFI runtime callbacks when we
shouldn't be. This patch just adds a check for efi_runtime_disabled in
uv_bios_init() so that we don't map in uv_systab when runtime_disabled ==

Signed-off-by: Alex Thorlton <>
Signed-off-by: Matt Fleming <>
Cc: Andy Lutomirski <>
Cc: Ard Biesheuvel <>
Cc: Borislav Petkov <>
Cc: Borislav Petkov <>
Cc: Brian Gerst <>
Cc: Denys Vlasenko <>
Cc: H. Peter Anvin <>
Cc: Josh Poimboeuf <>
Cc: Linus Torvalds <>
Cc: Mike Travis <>
Cc: Peter Zijlstra <>
Cc: Russ Anderson <>
Cc: Thomas Gleixner <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86/platform/uv/bios_uv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/platform/uv/bios_uv.c
+++ b/arch/x86/platform/uv/bios_uv.c
@@ -188,7 +188,8 @@ EXPORT_SYMBOL_GPL(uv_bios_set_legacy_vga
void uv_bios_init(void)
uv_systab = NULL;
- if ((efi.uv_systab == EFI_INVALID_TABLE_ADDR) || !efi.uv_systab) {
+ if ((efi.uv_systab == EFI_INVALID_TABLE_ADDR) ||
+ !efi.uv_systab || efi_runtime_disabled()) {
pr_crit("UV: UVsystab: missing\n");

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