linux-kernel - [RFC PATCH v6 03/11] x86/cet/ibt: Add IBT legacy code bitmap setup function

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Date:   Mon, 19 Nov 2018 13:49:26 -0800
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>,
        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>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [RFC PATCH v6 03/11] x86/cet/ibt: Add IBT legacy code bitmap setup function

Indirect Branch Tracking (IBT) provides an optional legacy code bitmap
that allows execution of legacy, non-IBT compatible library by an
IBT-enabled application.  When set, each bit in the bitmap indicates
one page of legacy code.

The bitmap is allocated and setup from the application.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 arch/x86/include/asm/cet.h |  1 +
 arch/x86/kernel/cet.c      | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
index 810d3e386fdb..db40fc54a905 100644
--- a/arch/x86/include/asm/cet.h
+++ b/arch/x86/include/asm/cet.h
@@ -29,6 +29,7 @@ void cet_disable_free_shstk(struct task_struct *p);
 int cet_restore_signal(unsigned long ssp);
 int cet_setup_signal(bool ia32, unsigned long rstor, unsigned long *new_ssp);
 int cet_setup_ibt(void);
+int cet_setup_ibt_bitmap(unsigned long bitmap, unsigned long size);
 void cet_disable_ibt(void);
 #else
 static inline int prctl_cet(int option, unsigned long arg2) { return -EINVAL; }
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
index fd157a6208c3..18a92a92c50f 100644
--- a/arch/x86/kernel/cet.c
+++ b/arch/x86/kernel/cet.c
@@ -21,6 +21,7 @@
 #include <asm/fpu/types.h>
 #include <asm/cet.h>
 #include <asm/special_insns.h>
+#include <asm/elf.h>
 
 static int set_shstk_ptr(unsigned long addr)
 {
@@ -333,3 +334,25 @@ void cet_disable_ibt(void)
 	wrmsrl(MSR_IA32_U_CET, r);
 	current->thread.cet.ibt_enabled = 0;
 }
+
+int cet_setup_ibt_bitmap(unsigned long bitmap, unsigned long size)
+{
+	u64 r;
+
+	if (!current->thread.cet.ibt_enabled)
+		return -EINVAL;
+
+	if (!PAGE_ALIGNED(bitmap) || (size > TASK_SIZE_MAX))
+		return -EINVAL;
+
+	current->thread.cet.ibt_bitmap_addr = bitmap;
+	current->thread.cet.ibt_bitmap_size = size;
+
+	/*
+	 * 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