From 87c19e8de4f56d803d133c3e38bbd7b069e06df3 Mon Sep 17 00:00:00 2001
From: Dave Young <dyoung@redhat.com>
Date: Fri, 9 Jun 2017 08:45:58 +0000
Subject: [PATCH] efi: Fix boot panic because of invalid BGRT image address

Maniaxx reported a kernel boot crash in the EFI code, which I emulated
by using same invalid phys addr in code:

  BUG: unable to handle kernel paging request at ffffffffff280001
  IP: efi_bgrt_init+0xfb/0x153
  ...
  Call Trace:
   ? bgrt_init+0xbc/0xbc
   acpi_parse_bgrt+0xe/0x12
   acpi_table_parse+0x89/0xb8
   acpi_boot_init+0x445/0x4e2
   ? acpi_parse_x2apic+0x79/0x79
   ? dmi_ignore_irq0_timer_override+0x33/0x33
   setup_arch+0xb63/0xc82
   ? early_idt_handler_array+0x120/0x120
   start_kernel+0xb7/0x443
   ? early_idt_handler_array+0x120/0x120
   x86_64_start_reservations+0x29/0x2b
   x86_64_start_kernel+0x154/0x177
   secondary_startup_64+0x9f/0x9f

There is also a similar bug filed in bugzilla.kernel.org:

  https://bugzilla.kernel.org/show_bug.cgi?id=195633

The crash is caused by this commit:

  7b0a911478c7 efi/x86: Move the EFI BGRT init code to early init code

The root cause is the firmware on those machines provides invalid BGRT
image addresses.

In a kernel before above commit BGRT initializes late and uses ioremap()
to map the image address. Ioremap validates the address, if it is not a
valid physical address ioremap() just fails and returns. However in current
kernel EFI BGRT initializes early and uses early_memremap() which does not
validate the image address, and kernel panic happens.

According to ACPI spec the BGRT image address should fall into
EFI_BOOT_SERVICES_DATA, see the section 5.2.22.4 of below document:

  http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf

Fix this issue by validating the image address in efi_bgrt_init(). If the
image address does not fall into any EFI_BOOT_SERVICES_DATA areas we just
bail out with a warning message.

Reported-by: Maniaxx <tripleshiftone@gmail.com>
Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Fixes: 7b0a911478c7 ("efi/x86: Move the EFI BGRT init code to early init code")
Link: http://lkml.kernel.org/r/20170609084558.26766-2-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[labbott@redhat.com: Backport to 4.11]
Signed-off-by: Laura Abbott <labbott@redhat.com>
---
 arch/x86/platform/efi/efi-bgrt.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/efi-bgrt.c
index 04ca876..08ee795 100644
--- a/arch/x86/platform/efi/efi-bgrt.c
+++ b/arch/x86/platform/efi/efi-bgrt.c
@@ -27,6 +27,26 @@ struct bmp_header {
 	u32 size;
 } __packed;
 
+static bool efi_bgrt_addr_valid(u64 addr)
+{
+	efi_memory_desc_t *md;
+
+	for_each_efi_memory_desc(md) {
+		u64 size;
+		u64 end;
+
+		if (md->type != EFI_BOOT_SERVICES_DATA)
+			continue;
+
+		size = md->num_pages << EFI_PAGE_SHIFT;
+		end = md->phys_addr + size;
+		if (addr >= md->phys_addr && addr < end)
+			return true;
+	}
+
+	return false;
+}
+
 void __init efi_bgrt_init(struct acpi_table_header *table)
 {
 	void *image;
@@ -62,6 +82,10 @@ void __init efi_bgrt_init(struct acpi_table_header *table)
 		goto out;
 	}
 
+	if (!efi_bgrt_addr_valid(bgrt->image_address)) {
+		pr_notice("Ignoring BGRT: invalid image address\n");
+		goto out;
+	}
 	image = early_memremap(bgrt->image_address, sizeof(bmp_header));
 	if (!image) {
 		pr_notice("Ignoring BGRT: failed to map image header memory\n");
-- 
2.7.5