linux-kernel - [PATCH 4.7 003/143] x86/platform/uv: Skip UV runtime services mapping in the efi_runtime

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Date:   Mon,  5 Sep 2016 18:42:59 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alex Thorlton <athorlton@....com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Borislav Petkov <bp@...en8.de>, Borislav Petkov <bp@...e.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Travis <travis@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Russ Anderson <rja@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
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 <athorlton@....com>

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.

Signed-off-by: Alex Thorlton <athorlton@....com>
Signed-off-by: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Travis <travis@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Russ Anderson <rja@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-efi@...r.kernel.org
Link: http://lkml.kernel.org/r/1470912120-22831-2-git-send-email-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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");
 		return;
 	}