linux-kernel - [RFC PATCH 3/3] Prevent user from writing to IBT bitmap.

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Date:   Fri, 28 Jun 2019 12:41:58 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [RFC PATCH 3/3] Prevent user from writing to IBT bitmap.

The IBT bitmap is visiable from user-mode, but not writable.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>

---
 arch/x86/mm/fault.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 59f4f66e4f2e..231196abb62e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1454,6 +1454,13 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 * we can handle it..
 	 */
 good_area:
+#define USER_MODE_WRITE (FAULT_FLAG_WRITE | FAULT_FLAG_USER)
+	if (((flags & USER_MODE_WRITE)  == USER_MODE_WRITE) &&
+	    (vma->vm_flags & VM_IBT)) {
+		bad_area_access_error(regs, hw_error_code, address, vma);
+		return;
+	}
+
 	if (unlikely(access_error(hw_error_code, vma))) {
 		bad_area_access_error(regs, hw_error_code, address, vma);
 		return;
-- 
2.17.1