Patch "x86/platform/uv: Skip UV runtime services mapping in the efi_runtime_disabled case" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

x86/platform/uv: Skip UV runtime services mapping in the efi_runtime_disabled case

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-platform-uv-skip-uv-runtime-services-mapping-in-the-efi_runtime_disabled-case.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alex Thorlton <[email protected]>
Date: Thu, 11 Aug 2016 11:41:59 +0100
Subject: x86/platform/uv: Skip UV runtime services mapping in the efi_runtime_disabled case

From: Alex Thorlton <[email protected]>

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 == true.

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

@@ -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");
 		return;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/x86-platform-uv-skip-uv-runtime-services-mapping-in-the-efi_runtime_disabled-case.patch