linux-kernel - [RFC][PATCH 2/3] x86_64: Allow breakpoints to emulate call functions

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Message-Id: <20190507174400.219947724@goodmis.org>
Date:   Tue, 07 May 2019 13:42:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, stable <stable@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [RFC][PATCH 2/3] x86_64: Allow breakpoints to emulate call functions

From: Peter Zijlstra <peterz@...radead.org>

In order to allow breakpoints to emulate call functions, they need to push
the return address onto the stack. But because the breakpoint exception
frame is added to the stack when the breakpoint is hit, there's no room to
add the address onto the stack and return to the address of the emulated
called funtion.

To handle this, copy the exception frame on entry of the breakpoint handler
and have leave a gap that can be used to add a return address to the stack
frame and return from the breakpoint to the emulated called function,
allowing for that called function to return back to the location after the
breakpoint was placed.

The helper functions were also added:

  int3_emulate_push(): to push the address onto the gap in the stack
  int3_emulate_jmp(): changes the location of the regs->ip to return there.
  int3_emulate_call(): push the return address and change regs->ip

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Nicolai Stange <nstange@...e.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: the arch/x86 maintainers <x86@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Jiri Kosina <jikos@...nel.org>
Cc: Miroslav Benes <mbenes@...e.cz>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Joe Lawrence <joe.lawrence@...hat.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Mimi Zohar <zohar@...ux.ibm.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Nayna Jain <nayna@...ux.ibm.com>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc: Joerg Roedel <jroedel@...e.de>
Cc: "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Cc: stable@...r.kernel.org
Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
[ Modified to only work for x86_64 ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 arch/x86/include/asm/text-patching.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index e85ff65c43c3..455bf9f88233 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -39,4 +39,26 @@ extern int poke_int3_handler(struct pt_regs *regs);
 extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
 extern int after_bootmem;
 
+static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
+{
+	regs->ip = ip;
+}
+
+#define INT3_INSN_SIZE 1
+#define CALL_INSN_SIZE 5
+
+#ifdef CONFIG_X86_64
+static inline void int3_emulate_push(struct pt_regs *regs, unsigned long val)
+{
+	regs->sp -= sizeof(unsigned long);
+	*(unsigned long *)regs->sp = val;
+}
+
+static inline void int3_emulate_call(struct pt_regs *regs, unsigned long func)
+{
+	int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
+	int3_emulate_jmp(regs, func);
+}
+#endif
+
 #endif /* _ASM_X86_TEXT_PATCHING_H */
-- 
2.20.1