From f72075c9eda8a43aeea2f9dbb8d187afd4a76f0b Mon Sep 17 00:00:00 2001 From: Alex Thorlton Date: Thu, 11 Aug 2016 11:41:59 +0100 Subject: [PATCH] x86/platform/uv: Skip UV runtime services mapping in the efi_runtime_disabled case 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: [] 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 Signed-off-by: Matt Fleming Cc: # v4.7 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 Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/1470912120-22831-2-git-send-email-matt@codeblueprint.co.uk Signed-off-by: Ingo Molnar --- arch/x86/platform/uv/bios_uv.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/platform/uv/bios_uv.c b/arch/x86/platform/uv/bios_uv.c index 66b2166ea4a1..0df8a0370d32 100644 --- a/arch/x86/platform/uv/bios_uv.c +++ b/arch/x86/platform/uv/bios_uv.c @@ -187,7 +187,8 @@ EXPORT_SYMBOL_GPL(uv_bios_set_legacy_vga_target); 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; }