From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Nicolai Stange <nstange@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
the arch/x86 maintainers <x86@kernel.org>,
Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
Petr Mladek <pmladek@suse.com>,
Joe Lawrence <joe.lawrence@redhat.com>,
Shuah Khan <shuah@kernel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Mimi Zohar <zohar@linux.ibm.com>, Juergen Gross <jgross@suse.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Nayna Jain <nayna@linux.ibm.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Joerg Roedel <jroedel@suse.de>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
stable <stable@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [RFC][PATCH 2/3] x86_64: Allow breakpoints to emulate call functions
Date: Tue, 7 May 2019 12:53:42 -0500 [thread overview]
Message-ID: <20190507175342.fskdj2qidpao65qi@treble> (raw)
In-Reply-To: <20190507174400.219947724@goodmis.org>
On Tue, May 07, 2019 at 01:42:29PM -0400, Steven Rostedt wrote:
> From: Peter Zijlstra <peterz@infradead.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.
This part is done by patch 1.
>
> The helper functions were also added:
No longer "also" :-)
> 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@kernel.org>
> Cc: Nicolai Stange <nstange@suse.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: the arch/x86 maintainers <x86@kernel.org>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Jiri Kosina <jikos@kernel.org>
> Cc: Miroslav Benes <mbenes@suse.cz>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Joe Lawrence <joe.lawrence@redhat.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Tim Chen <tim.c.chen@linux.intel.com>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Mimi Zohar <zohar@linux.ibm.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Nayna Jain <nayna@linux.ibm.com>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>
> Cc: stable@vger.kernel.org
> Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> [ Modified to only work for x86_64 ]
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.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;
> +}
How this works isn't really obvious. A comment is probably warranted to
explain the fact that the int3 entry code reserved some space on the
stack.
--
Josh
next prev parent reply other threads:[~2019-05-07 17:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-07 17:42 [RFC][PATCH 0/3] x86_64/ftrace: Emulate calls from int3 when patching functions Steven Rostedt
2019-05-07 17:42 ` [RFC][PATCH 1/3] x86_64: Add gap to int3 to allow for call emulation Steven Rostedt
2019-05-07 17:56 ` Josh Poimboeuf
2019-05-07 18:57 ` Steven Rostedt
2019-05-07 17:42 ` [RFC][PATCH 2/3] x86_64: Allow breakpoints to emulate call functions Steven Rostedt
2019-05-07 17:53 ` Josh Poimboeuf [this message]
2019-05-07 19:01 ` Steven Rostedt
2019-05-07 19:14 ` Josh Poimboeuf
2019-05-07 19:20 ` Steven Rostedt
2019-05-07 19:49 ` Josh Poimboeuf
2019-05-07 19:58 ` Steven Rostedt
2019-05-07 20:02 ` Josh Poimboeuf
2019-05-07 17:42 ` [RFC][PATCH 3/3] ftrace/x86_64: Emulate call function while updating in breakpoint handler Steven Rostedt
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