linux-kernel - [PATCH v3 4/5] Add taint flag for TDX overrides

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Date:   Thu,  5 Aug 2021 16:30:35 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     "H . Peter Anvin" <hpa@...or.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>
Subject: [PATCH v3 4/5] Add taint flag for TDX overrides

From: Andi Kleen <ak@...ux.intel.com>

Add a new taint flag TAINT_CONF_NO_LOCKDOWN that is set when
the default hardening against untrusted hosts in TDX is overridden
on the command line. The flag is set when the device or ACPI
filters are disabled.

The main use cases is for applications to detect that they
might run in a potentially insecure configuration through
/proc/sys/kernel/taint.

The setting is not intended for attestation, which should attest the
kernel command line anyways.

I picked 'Y' for the oops flag, although this type of taint is probably
not too useful for crashes, since there weren't any other good letters
left.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
---
 Documentation/admin-guide/tainted-kernels.rst | 7 ++++++-
 include/linux/panic.h                         | 3 ++-
 kernel/panic.c                                | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
index ceeed7b0798d..65c58092ec35 100644
--- a/Documentation/admin-guide/tainted-kernels.rst
+++ b/Documentation/admin-guide/tainted-kernels.rst
@@ -100,7 +100,8 @@ Bit  Log  Number  Reason that got the kernel tainted
  15  _/K   32768  kernel has been live patched
  16  _/X   65536  auxiliary taint, defined for and used by distros
  17  _/T  131072  kernel was built with the struct randomization plugin
-===  ===  ======  ========================================================
+ 18  _/Y  262144  confidential guest (like TDX guest) without full lockdown
+===  ===  ======  =========================================================
 
 Note: The character ``_`` is representing a blank in this table to make reading
 easier.
@@ -175,3 +176,7 @@ More detailed explanation for tainting
      produce extremely unusual kernel structure layouts (even performance
      pathological ones), which is important to know when debugging. Set at
      build time.
+
+ 18) ``Y`` Kernel is running as a confidential guest on a untrusted
+     hypervisor (e.g. TDX), but has disabled some lock down options that could
+     make the kernel attackable from the host.
diff --git a/include/linux/panic.h b/include/linux/panic.h
index f5844908a089..9ac10689a432 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -74,7 +74,8 @@ static inline void set_arch_panic_timeout(int timeout, int arch_default_timeout)
 #define TAINT_LIVEPATCH			15
 #define TAINT_AUX			16
 #define TAINT_RANDSTRUCT		17
-#define TAINT_FLAGS_COUNT		18
+#define TAINT_CONF_NO_LOCKDOWN		18
+#define TAINT_FLAGS_COUNT		19
 #define TAINT_FLAGS_MAX			((1UL << TAINT_FLAGS_COUNT) - 1)
 
 struct taint_flag {
diff --git a/kernel/panic.c b/kernel/panic.c
index edad89660a2b..1557f864bec0 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -387,6 +387,7 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
 	[ TAINT_LIVEPATCH ]		= { 'K', ' ', true },
 	[ TAINT_AUX ]			= { 'X', ' ', true },
 	[ TAINT_RANDSTRUCT ]		= { 'T', ' ', true },
+	[ TAINT_CONF_NO_LOCKDOWN ]	= { 'Y', ' ', true },
 };
 
 /**
-- 
2.25.1