[PATCH V33 21/30] x86/mmiotrace: Lock down the testmmiotrace module

[Matthew Garrett]

From: David Howells <dhowe...@redhat.com>

The testmmiotrace module shouldn't be permitted when the kernel is locked
down as it can be used to arbitrarily read and write MMIO space. This is
a runtime check rather than buildtime in order to allow configurations
where the same kernel may be run in both locked down or permissive modes
depending on local policy.

Suggested-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: David Howells <dhowe...@redhat.com
Signed-off-by: Matthew Garrett <mj...@google.com>
cc: Thomas Gleixner <t...@linutronix.de>
cc: Steven Rostedt <rost...@goodmis.org>
cc: Ingo Molnar <mi...@kernel.org>
cc: "H. Peter Anvin" <h...@zytor.com>
cc: x...@kernel.org
---
 arch/x86/mm/testmmiotrace.c  | 3 +++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 5 insertions(+)

diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
index f6ae6830b341..a6b204f9f505 100644
--- a/arch/x86/mm/testmmiotrace.c
+++ b/arch/x86/mm/testmmiotrace.c
@@ -115,6 +115,9 @@ static int __init init(void)
 {
        unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
 
+       if (security_is_locked_down(LOCKDOWN_MMIOTRACE))
+               return -EPERM;
+
        if (mmio_address == 0) {
                pr_err("you have to use the module argument mmio_address.\n");
                pr_err("DO NOT LOAD THIS MODULE UNLESS YOU REALLY KNOW WHAT YOU 
ARE DOING!\n");
diff --git a/include/linux/security.h b/include/linux/security.h
index 47ca04ac00f6..89b7adfae525 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -93,6 +93,7 @@ enum lockdown_reason {
        LOCKDOWN_PCMCIA_CIS,
        LOCKDOWN_TIOCSSERIAL,
        LOCKDOWN_MODULE_PARAMETERS,
+       LOCKDOWN_MMIOTRACE,
        LOCKDOWN_INTEGRITY_MAX,
        LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 0788d4805449..215615e67237 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -29,6 +29,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] 
= {
        [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
        [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
        [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
+       [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
        [LOCKDOWN_INTEGRITY_MAX] = "integrity",
        [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
-- 
2.22.0.410.gd8fdbe21b5-goog