linux-kernel - Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions

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Date:   Mon, 28 Feb 2022 15:07:05 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        keescook@...omium.org, samitolvanen@...gle.com,
        mark.rutland@....com, alyssa.milburn@...el.com, mbenes@...e.cz,
        rostedt@...dmis.org, mhiramat@...nel.org,
        alexei.starovoitov@...il.com
Subject: Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions

Hi Peter,

So, instead of this change, can you try below?
This introduce the arch_adjust_kprobe_addr() and use it in the kprobe_addr()
so that it can handle the case that user passed the probe address in 
_text+OFFSET format.

From: Masami Hiramatsu <mhiramat@...nel.org>
Date: Mon, 28 Feb 2022 15:01:48 +0900
Subject: [PATCH] x86: kprobes: Skip ENDBR instruction probing

This adjust the kprobe probe address to skip the ENDBR and put the kprobe
next to the ENDBR so that the kprobe doesn't disturb IBT.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 arch/x86/kernel/kprobes/core.c |  7 +++++++
 include/linux/kprobes.h        |  2 ++
 kernel/kprobes.c               | 11 ++++++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 745f42cf82dc..a90cfe50d800 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -52,6 +52,7 @@
 #include <asm/insn.h>
 #include <asm/debugreg.h>
 #include <asm/set_memory.h>
+"include <asm/ibt.h>
 
 #include "common.h"
 
@@ -301,6 +302,12 @@ static int can_probe(unsigned long paddr)
 	return (addr == paddr);
 }
 
+/* If the x86 support IBT (ENDBR) it must be skipped. */
+kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr)
+{
+	return (kprobe_opcode_t *)skip_endbr((void *)addr);
+}
+
 /*
  * Copy an instruction with recovering modified instruction by kprobes
  * and adjust the displacement if the instruction uses the %rip-relative
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 19b884353b15..485d7832a613 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -384,6 +384,8 @@ static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void)
 }
 
 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset);
+kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr);
+
 int register_kprobe(struct kprobe *p);
 void unregister_kprobe(struct kprobe *p);
 int register_kprobes(struct kprobe **kps, int num);
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 94cab8c9ce56..312f10e85c93 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1488,6 +1488,15 @@ bool within_kprobe_blacklist(unsigned long addr)
 	return false;
 }
 
+/*
+ * If the arch supports the feature like IBT which will put a trap at
+ * the entry of the symbol, it must be adjusted in this function.
+ */
+kprobe_opcode_t *__weak arch_adjust_kprobe_addr(unsigned long addr)
+{
+	return (kprobe_opcode_t *)addr;
+}
+
 /*
  * If 'symbol_name' is specified, look it up and add the 'offset'
  * to it. This way, we can specify a relative address to a symbol.
@@ -1506,7 +1515,7 @@ static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr,
 			return ERR_PTR(-ENOENT);
 	}
 
-	addr = (kprobe_opcode_t *)(((char *)addr) + offset);
+	addr = arch_adjust_kprobe_addr((unsigned long)addr + offset);
 	if (addr)
 		return addr;
 
-- 
2.25.1


On Thu, 24 Feb 2022 15:51:53 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> With IBT on, sym+0 is no longer the __fentry__ site.
> 
> NOTE: the architecture has a special case and *does* allow placing an
> INT3 breakpoint over ENDBR in which case #BP has precedence over #CP
> and as such we don't need to disallow probing these instructions.
> 
> NOTE: irrespective of the above; there is a complication in that
> direct branches to functions are rewritten to not execute ENDBR, so
> any breakpoint thereon might miss lots of actual function executions.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/kernel/kprobes/core.c |   11 +++++++++++
>  kernel/kprobes.c               |   15 ++++++++++++---
>  2 files changed, 23 insertions(+), 3 deletions(-)
> 
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -1156,3 +1162,8 @@ int arch_trampoline_kprobe(struct kprobe
>  {
>  	return 0;
>  }
> +
> +bool arch_kprobe_on_func_entry(unsigned long offset)
> +{
> +	return offset <= 4*HAS_KERNEL_IBT;
> +}
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -67,10 +67,19 @@ static bool kprobes_all_disarmed;
>  static DEFINE_MUTEX(kprobe_mutex);
>  static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);
>  
> -kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
> -					unsigned int __unused)
> +kprobe_opcode_t * __weak kprobe_lookup_name(const char *name, unsigned int offset)
>  {
> -	return ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
> +	kprobe_opcode_t *addr = NULL;
> +
> +	addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
> +#ifdef CONFIG_KPROBES_ON_FTRACE
> +	if (addr && !offset) {
> +		unsigned long faddr = ftrace_location((unsigned long)addr);
> +		if (faddr)
> +			addr = (kprobe_opcode_t *)faddr;
> +	}
> +#endif
> +	return addr;
>  }
>  
>  /*
> 
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>