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From: Kees Cook <keescook@chromium.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Matthew Garrett <matthew.garrett@nebula.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, linux-efi@vger.kernel.org,
	linux-security-module <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH] x86: Lock down MSR writing in secure boot
Date: Fri, 8 Feb 2013 11:18:54 -0800	[thread overview]
Message-ID: <CAGXu5jJnLY6Qp3J6HBpVg-AdUGdKYm-e4wErZO3=NuRo04ajvg@mail.gmail.com> (raw)
In-Reply-To: <00780235-deac-4f80-b936-867834e05661@email.android.com>

No. CAP_RAWIO is for reading. Writing needs a much stronger check.

-Kees

On Fri, Feb 8, 2013 at 11:17 AM, H. Peter Anvin <hpa@zytor.com> wrote:
> We already have CAP_RAWIO for this in mainline; I am not sure if this should be harder than that...
>
> Kees Cook <keescook@chromium.org> wrote:
>
>>Writing to MSRs should not be allowed unless CAP_COMPROMISE_KERNEL is
>>set since it could lead to execution of arbitrary code in kernel mode.
>>
>>Signed-off-by: Kees Cook <keescook@chromium.org>
>>---
>>This would be used on top of Matthew Garrett's existing "Secure boot
>>policy support" patch series.
>>---
>> arch/x86/kernel/msr.c |    7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>>diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
>>index 4929502..adaab3d 100644
>>--- a/arch/x86/kernel/msr.c
>>+++ b/arch/x86/kernel/msr.c
>>@@ -103,6 +103,9 @@ static ssize_t msr_write(struct file *file, const
>>char __user *buf,
>>       int err = 0;
>>       ssize_t bytes = 0;
>>
>>+      if (!capable(CAP_COMPROMISE_KERNEL))
>>+              return -EPERM;
>>+
>>       if (count % 8)
>>               return -EINVAL; /* Invalid chunk size */
>>
>>@@ -150,6 +153,10 @@ static long msr_ioctl(struct file *file, unsigned
>>int ioc, unsigned long arg)
>>                       err = -EBADF;
>>                       break;
>>               }
>>+              if (!capable(CAP_COMPROMISE_KERNEL)) {
>>+                      err = -EPERM;
>>+                      break;
>>+              }
>>               if (copy_from_user(&regs, uregs, sizeof regs)) {
>>                       err = -EFAULT;
>>                       break;
>
> --
> Sent from my mobile phone. Please excuse brevity and lack of formatting.



--
Kees Cook
Chrome OS Security

  reply	other threads:[~2013-02-08 19:18 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-02-08 19:12 Kees Cook
2013-02-08 19:17 ` H. Peter Anvin
2013-02-08 19:18   ` Kees Cook [this message]
2013-02-08 19:42     ` H. Peter Anvin
2013-02-08 20:14       ` Kees Cook
2013-02-08 20:18         ` H. Peter Anvin
2013-02-08 20:28           ` Kees Cook
2013-02-08 20:34             ` Matthew Garrett
2013-02-08 21:02               ` Kees Cook
2013-02-08 21:07                 ` Matthew Garrett
2013-02-08 21:14                   ` Josh Boyer
2013-02-08 23:09                     ` Andy Lutomirski
2013-02-08 22:30                 ` H. Peter Anvin
2013-02-08 23:06                   ` Borislav Petkov
2013-02-08 23:26                     ` Matthew Garrett
2013-02-09  1:22                       ` H. Peter Anvin
2013-02-09  1:29                         ` Matthew Garrett
2013-02-09  6:45                           ` Kees Cook
2013-02-09  9:29                             ` Borislav Petkov
2013-02-09 15:10                               ` Kees Cook
2013-02-09 15:11                               ` Matthew Garrett
2013-02-13  0:48                                 ` H. Peter Anvin
2013-02-13  5:39                                   ` Matthew Garrett
2013-02-13  6:12                                     ` H. Peter Anvin
2013-02-13  6:27                                       ` Matthew Garrett
2013-02-13  6:33                                         ` H. Peter Anvin
2013-02-13  6:41                                           ` Matthew Garrett
2013-02-13 17:20                                             ` H. Peter Anvin
2013-02-13 17:26                                               ` Matthew Garrett
2013-02-13 17:51                                                 ` Casey Schaufler
2013-02-13 17:56                                                   ` Matthew Garrett
2013-02-13 18:44                                                     ` H. Peter Anvin
2013-02-13 18:51                                                       ` Matthew Garrett
2013-02-13 22:26                                                   ` H. Peter Anvin
2013-02-13 22:58                                                     ` Casey Schaufler
2013-02-14  0:25                                                       ` H. Peter Anvin
2013-02-14  0:44                                                         ` Casey Schaufler
2013-02-14  1:04                                                           ` Matthew Garrett
2013-02-14  1:08                                                             ` H. Peter Anvin
2013-02-14  2:46                                                               ` Matthew Garrett
2013-02-14  1:34                                                             ` Casey Schaufler
2013-02-13  8:27                                           ` Paolo Bonzini
2013-02-13 17:21                                             ` H. Peter Anvin
2013-02-13 17:22                                             ` H. Peter Anvin
2013-02-13 19:55                                               ` Paolo Bonzini
2013-02-13 22:24                                                 ` H. Peter Anvin
2013-02-08 19:17 ` Matthew Garrett
2013-02-08 19:21   ` Kees Cook
2013-02-08 19:27     ` Matthew Garrett

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