[PATCH V40 20/29] 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>
Acked-by: Steven Rostedt (VMware) <rost...@goodmis.org>
Reviewed-by: Kees Cook <keesc...@chromium.org>
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
Signed-off-by: James Morris <jmor...@namei.org>
---
 arch/x86/mm/testmmiotrace.c  | 5 +++++
 include/linux/security.h     | 1 +
 security/lockdown/lockdown.c | 1 +
 3 files changed, 7 insertions(+)

diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
index 0881e1ff1e58..a8bd952e136d 100644
--- a/arch/x86/mm/testmmiotrace.c
+++ b/arch/x86/mm/testmmiotrace.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/io.h>
 #include <linux/mmiotrace.h>
+#include <linux/security.h>
 
 static unsigned long mmio_address;
 module_param_hw(mmio_address, ulong, iomem, 0);
@@ -115,6 +116,10 @@ static void do_test_bulk_ioremapping(void)
 static int __init init(void)
 {
        unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
+       int ret = security_locked_down(LOCKDOWN_MMIOTRACE);
+
+       if (ret)
+               return ret;
 
        if (mmio_address == 0) {
                pr_err("you have to use the module argument mmio_address.\n");
diff --git a/include/linux/security.h b/include/linux/security.h
index 1a3404f9c060..d8db7ea4c4bf 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -114,6 +114,7 @@ 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 0fa434294667..2eadbe0667e7 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",
 };
-- 
2.23.0.rc1.153.gdeed80330f-goog