linux-kernel - [PATCH 4.4 11/47] kprobes/x86: Do not modify singlestep buffer while resuming

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Date:   Tue, 10 Jul 2018 20:24:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ye Xiaolong <xiaolong.ye@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Alexey Makhalov <amakhalov@...are.com>
Subject: [PATCH 4.4 11/47] kprobes/x86: Do not modify singlestep buffer while resuming

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@...nel.org>

commit 804dec5bda9b4fcdab5f67fe61db4a0498af5221 upstream.

Do not modify singlestep execution buffer (kprobe.ainsn.insn)
while resuming from single-stepping, instead, modifies
the buffer to add a jump back instruction at preparing
buffer.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David S . Miller <davem@...emloft.net>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ye Xiaolong <xiaolong.ye@...el.com>
Link: http://lkml.kernel.org/r/149076361560.22469.1610155860343077495.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Signed-off-by: Alexey Makhalov <amakhalov@...are.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/kprobes/core.c |   42 +++++++++++++++++++----------------------
 1 file changed, 20 insertions(+), 22 deletions(-)

--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -411,25 +411,38 @@ void free_insn_page(void *page)
 	module_memfree(page);
 }
 
+/* Prepare reljump right after instruction to boost */
+static void prepare_boost(struct kprobe *p, int length)
+{
+	if (can_boost(p->ainsn.insn, p->addr) &&
+	    MAX_INSN_SIZE - length >= RELATIVEJUMP_SIZE) {
+		/*
+		 * These instructions can be executed directly if it
+		 * jumps back to correct address.
+		 */
+		synthesize_reljump(p->ainsn.insn + length, p->addr + length);
+		p->ainsn.boostable = 1;
+	} else {
+		p->ainsn.boostable = -1;
+	}
+}
+
 static int arch_copy_kprobe(struct kprobe *p)
 {
-	int ret;
+	int len;
 
 	set_memory_rw((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
 
 	/* Copy an instruction with recovering if other optprobe modifies it.*/
-	ret = __copy_instruction(p->ainsn.insn, p->addr);
-	if (!ret)
+	len = __copy_instruction(p->ainsn.insn, p->addr);
+	if (!len)
 		return -EINVAL;
 
 	/*
 	 * __copy_instruction can modify the displacement of the instruction,
 	 * but it doesn't affect boostable check.
 	 */
-	if (can_boost(p->ainsn.insn, p->addr))
-		p->ainsn.boostable = 0;
-	else
-		p->ainsn.boostable = -1;
+	prepare_boost(p, len);
 
 	set_memory_ro((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
 
@@ -894,21 +907,6 @@ static void resume_execution(struct kpro
 		break;
 	}
 
-	if (p->ainsn.boostable == 0) {
-		if ((regs->ip > copy_ip) &&
-		    (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) {
-			/*
-			 * These instructions can be executed directly if it
-			 * jumps back to correct address.
-			 */
-			synthesize_reljump((void *)regs->ip,
-				(void *)orig_ip + (regs->ip - copy_ip));
-			p->ainsn.boostable = 1;
-		} else {
-			p->ainsn.boostable = -1;
-		}
-	}
-
 	regs->ip += orig_ip - copy_ip;
 
 no_change: