From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Jiri Olsa <jolsa@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
lkml <linux-kernel@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
"Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH v13 bpf-next 1/1] rethook: x86: Add rethook x86 implementation
Date: Wed, 23 Mar 2022 09:05:26 +0100 [thread overview]
Message-ID: <YjrUxmABaohh1I8W@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <164800289923.1716332.9772144337267953560.stgit@devnote2>
On Wed, Mar 23, 2022 at 11:34:59AM +0900, Masami Hiramatsu wrote:
> Add rethook for x86 implementation. Most of the code has been copied from
> kretprobes on x86.
Right; as said, I'm really unhappy with growing a carbon copy of this
stuff instead of sharing. Can we *please* keep it a single instance?
Them being basically indentical, it should be trivial to have
CONFIG_KPROBE_ON_RETHOOK (or somesuch) and just share this.
Also, what's rethook for anyway?
> diff --git a/arch/x86/kernel/kprobes/common.h b/arch/x86/kernel/kprobes/common.h
> index 7d3a2e2daf01..c993521d4933 100644
> --- a/arch/x86/kernel/kprobes/common.h
> +++ b/arch/x86/kernel/kprobes/common.h
> @@ -6,6 +6,7 @@
>
> #include <asm/asm.h>
> #include <asm/frame.h>
> +#include <asm/insn.h>
>
> #ifdef CONFIG_X86_64
>
> diff --git a/arch/x86/kernel/rethook.c b/arch/x86/kernel/rethook.c
> new file mode 100644
> index 000000000000..3e916361c33b
> --- /dev/null
> +++ b/arch/x86/kernel/rethook.c
> @@ -0,0 +1,121 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
> + */
> +#include <linux/bug.h>
> +#include <linux/rethook.h>
> +#include <linux/kprobes.h>
> +#include <linux/objtool.h>
> +
> +#include "kprobes/common.h"
> +
> +__visible void arch_rethook_trampoline_callback(struct pt_regs *regs);
> +
> +/*
> + * When a target function returns, this code saves registers and calls
> + * arch_rethook_trampoline_callback(), which calls the rethook handler.
> + */
> +asm(
> + ".text\n"
> + ".global arch_rethook_trampoline\n"
> + ".type arch_rethook_trampoline, @function\n"
> + "arch_rethook_trampoline:\n"
> +#ifdef CONFIG_X86_64
> + ANNOTATE_NOENDBR /* This is only jumped from ret instruction */
> + /* Push a fake return address to tell the unwinder it's a kretprobe. */
> + " pushq $arch_rethook_trampoline\n"
> + UNWIND_HINT_FUNC
" pushq $" __stringify(__KERNEL_DS) "\n" /* %ss */
/* Save the 'sp - 16', this will be fixed later. */
> + " pushq %rsp\n"
> + " pushfq\n"
> + SAVE_REGS_STRING
> + " movq %rsp, %rdi\n"
> + " call arch_rethook_trampoline_callback\n"
> + RESTORE_REGS_STRING
/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
this comment could do with a 'why' though... Because neither
this nor the one in the handler really explains why it is
important to have popf last
" addq $16, %rsp\n"
> + " popfq\n"
> +#else
same for i386:
> + /* Push a fake return address to tell the unwinder it's a kretprobe. */
> + " pushl $arch_rethook_trampoline\n"
> + UNWIND_HINT_FUNC
/* Save the 'sp - 8', this will be fixed later. */
" pushl %ss\n"
> + " pushl %esp\n"
> + " pushfl\n"
> + SAVE_REGS_STRING
> + " movl %esp, %eax\n"
> + " call arch_rethook_trampoline_callback\n"
> + RESTORE_REGS_STRING
/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
" addl $8, %esp\n"
> + " popfl\n"
> +#endif
> + ASM_RET
> + ".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
> +);
> +NOKPROBE_SYMBOL(arch_rethook_trampoline);
> +
> +/*
> + * Called from arch_rethook_trampoline
> + */
> +__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
> +{
> + unsigned long *frame_pointer;
> +
> + /* fixup registers */
> + regs->cs = __KERNEL_CS;
> +#ifdef CONFIG_X86_32
> + regs->gs = 0;
> +#endif
> + regs->ip = (unsigned long)&arch_rethook_trampoline;
> + regs->orig_ax = ~0UL;
regs->sp += 2*sizeof(long);
> + frame_pointer = ®s->sp + 1;
> +
> + /*
> + * The return address at 'frame_pointer' is recovered by the
> + * arch_rethook_fixup_return() which called from this
> + * rethook_trampoline_handler().
> + */
> + rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
> +
> + /*
> + * Copy FLAGS to 'pt_regs::sp' so that arch_rethook_trapmoline()
> + * can do RET right after POPF.
> + */
regs->ss = regs->flags;
> +}
> +NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
next prev parent reply other threads:[~2022-03-23 8:06 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-23 2:34 [PATCH v13 bpf-next 0/1] fprobe: Introduce fprobe function entry/exit probe Masami Hiramatsu
2022-03-23 2:34 ` [PATCH v13 bpf-next 1/1] rethook: x86: Add rethook x86 implementation Masami Hiramatsu
2022-03-23 8:05 ` Peter Zijlstra [this message]
2022-03-23 11:41 ` Masami Hiramatsu
2022-03-23 12:34 ` Peter Zijlstra
2022-03-23 15:14 ` Masami Hiramatsu
2022-03-25 2:03 ` Alexei Starovoitov
2022-03-25 2:21 ` Masami Hiramatsu
2022-03-25 2:41 ` Alexei Starovoitov
2022-03-23 5:42 ` [PATCH v13 bpf-next 0/1] fprobe: Introduce fprobe function entry/exit probe Masami Hiramatsu
2022-03-23 14:18 ` Mark Rutland
2022-03-23 14:55 ` Masami Hiramatsu
2022-03-23 16:47 ` Mark Rutland
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