Patch "x86/efi: Always map the first physical page into the EFI pagetables" has been added to the 4.9-stable tree

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

x86/efi: Always map the first physical page into the EFI pagetables

to the 4.9-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-efi-always-map-the-first-physical-page-into-the-efi-pagetables.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Jiri Kosina <[email protected]>
Date: Fri, 27 Jan 2017 22:25:52 +0000
Subject: x86/efi: Always map the first physical page into the EFI pagetables

From: Jiri Kosina <[email protected]>

commit bf29bddf0417a4783da3b24e8c9e017ac649326f upstream.

Commit:

129766708 ("x86/efi: Only map RAM into EFI page tables if in mixed-mode")

stopped creating 1:1 mappings for all RAM, when running in native 64-bit mode.

It turns out though that there are 64-bit EFI implementations in the wild (this particular problem has been reported on a Lenovo Yoga 710-11IKB), which still make use of the first physical page for their own private use, even though they explicitly mark it EFI_CONVENTIONAL_MEMORY in the memory map.

In case there is no mapping for this particular frame in the EFI pagetables, as soon as firmware tries to make use of it, a triple fault occurs and the system reboots (in case of the Yoga 710-11IKB this is very early during bootup).

Fix that by always mapping the first page of physical memory into the EFI pagetables. We're free to hand this page to the BIOS, as trim_bios_range() will reserve the first page and isolate it away from memory allocators anyway.

Note that just reverting 129766708 alone is not enough on v4.9-rc1+ to fix the regression on affected hardware, as this commit:

ab72a27da ("x86/efi: Consolidate region mapping logic")

later made the first physical frame not to be mapped anyway.

---
 arch/x86/platform/efi/efi_64.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

@@ -269,6 +269,22 @@ int __init efi_setup_page_tables(unsigne
 	efi_scratch.use_pgd = true;
 
 	/*
+	 * Certain firmware versions are way too sentimential and still believe
+	 * they are exclusive and unquestionable owners of the first physical page,
+	 * even though they explicitly mark it as EFI_CONVENTIONAL_MEMORY
+	 * (but then write-access it later during SetVirtualAddressMap()).
+	 *
+	 * Create a 1:1 mapping for this page, to avoid triple faults during early
+	 * boot with such firmware. We are free to hand this page to the BIOS,
+	 * as trim_bios_range() will reserve the first page and isolate it away
+	 * from memory allocators anyway.
+	 */
+	if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
+		pr_err("Failed to create 1:1 mapping for the first page!\n");
+		return 1;
+	}
+
+	/*
 	 * When making calls to the firmware everything needs to be 1:1
 	 * mapped and addressable with 32-bit pointers. Map the kernel
 	 * text and allocate a new stack because we can't rely on the

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

queue-4.9/hid-cp2112-fix-gpio-callback-error-handling.patch queue-4.9/hid-cp2112-fix-sleep-while-atomic.patch queue-4.9/x86-efi-always-map-the-first-physical-page-into-the-efi-pagetables.patch