linux-kernel - [RFC PATCH v4 3/9] x86/cet/ibt: Add IBT legacy code bitmap allocation function

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Date:   Fri, 21 Sep 2018 08:05:47 -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>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.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>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [RFC PATCH v4 3/9] x86/cet/ibt: Add IBT legacy code bitmap allocation function

Indirect branch tracking provides an optional legacy code bitmap
that indicates locations of non-IBT compatible code.  When set,
each bit in the bitmap represents a page in the linear address is
legacy code.

We allocate the bitmap only when the application requests it.
Most applications do not need the bitmap.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 arch/x86/kernel/cet.c | 45 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index 6adfe795d692..a65d9745af08 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -314,3 +314,48 @@ void cet_disable_ibt(void)
 	wrmsrl(MSR_IA32_U_CET, r);
 	current->thread.cet.ibt_enabled = 0;
 }
+
+int cet_setup_ibt_bitmap(void)
+{
+	u64 r;
+	unsigned long bitmap;
+	unsigned long size;
+
+	if (!cpu_feature_enabled(X86_FEATURE_IBT))
+		return -EOPNOTSUPP;
+
+	if (!current->thread.cet.ibt_bitmap_addr) {
+		/*
+		 * Calculate size and put in thread header.
+		 * may_expand_vm() needs this information.
+		 */
+		size = TASK_SIZE / PAGE_SIZE / BITS_PER_BYTE;
+		current->thread.cet.ibt_bitmap_size = size;
+		bitmap = do_mmap_locked(0, size, PROT_READ | PROT_WRITE,
+					MAP_ANONYMOUS | MAP_PRIVATE,
+					VM_DONTDUMP);
+
+		if (bitmap >= TASK_SIZE) {
+			current->thread.cet.ibt_bitmap_size = 0;
+			return -ENOMEM;
+		}
+
+		current->thread.cet.ibt_bitmap_addr = bitmap;
+	}
+
+	/*
+	 * Lower bits of MSR_IA32_CET_LEG_IW_EN are for IBT
+	 * settings.  Clear lower bits even bitmap is already
+	 * page-aligned.
+	 */
+	bitmap = current->thread.cet.ibt_bitmap_addr;
+	bitmap &= PAGE_MASK;
+
+	/*
+	 * Turn on IBT legacy bitmap.
+	 */
+	rdmsrl(MSR_IA32_U_CET, r);
+	r |= (MSR_IA32_CET_LEG_IW_EN | bitmap);
+	wrmsrl(MSR_IA32_U_CET, r);
+	return 0;
+}
-- 
2.17.1