linux-kernel - Re: [PATCH] x86/unwind/orc: Handle kretprobes

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Date:   Mon, 11 Oct 2021 14:03:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Marios Pomonis <pomonis@...gle.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Kristen C Accardi <kristen.c.accardi@...el.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ivan Babrou <ivan@...udflare.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Julien Thierry <jthierry@...hat.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] x86/unwind/orc: Handle kretprobes_trampoline

On Thu, Sep 02, 2021 at 07:13:26PM -0700, Kees Cook wrote:
> From: Marios Pomonis <pomonis@...gle.com>
> 
> Fix a bug in the ORC unwinder when kretprobes has replaced a return
> address with the address of `kretprobes_trampoline'. ORC mistakenly
> assumes that the address in the stack is a return address and decrements
> it by 1 in order to find the proper depth of the next frame.
> 
> This issue was discovered while testing the FG-KASLR series[0][1] and
> running the live patching test[2] that was originally failing[3].
> 
> [0] https://lore.kernel.org/kernel-hardening/20200923173905.11219-1-kristen@linux.intel.com/
> [1] https://github.com/KSPP/linux/issues/132
> [2] https://github.com/lpechacek/qa_test_klp
> [3] https://lore.kernel.org/lkml/alpine.LSU.2.21.2009251450260.13615@pobox.suse.cz/
> 
> Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
> Signed-off-by: Marios Pomonis <pomonis@...gle.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
> Cc: Kristen C Accardi <kristen.c.accardi@...el.com>
> Cc: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Ping again; Josh can you take this please?

-Kees

> ---
>  arch/x86/kernel/unwind_orc.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
> index a1202536fc57..8c5038b3b707 100644
> --- a/arch/x86/kernel/unwind_orc.c
> +++ b/arch/x86/kernel/unwind_orc.c
> @@ -7,6 +7,7 @@
>  #include <asm/unwind.h>
>  #include <asm/orc_types.h>
>  #include <asm/orc_lookup.h>
> +#include <asm/kprobes.h>
>  
>  #define orc_warn(fmt, ...) \
>  	printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
> @@ -414,6 +415,15 @@ static bool get_reg(struct unwind_state *state, unsigned int reg_off,
>  	return false;
>  }
>  
> +static bool is_kretprobe_trampoline(unsigned long ip)
> +{
> +#ifdef	CONFIG_KRETPROBES
> +	if (ip == (unsigned long)&kretprobe_trampoline)
> +		return true;
> +#endif
> +	return false;
> +}
> +
>  bool unwind_next_frame(struct unwind_state *state)
>  {
>  	unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
> @@ -540,7 +550,7 @@ bool unwind_next_frame(struct unwind_state *state)
>  		state->sp = sp;
>  		state->regs = NULL;
>  		state->prev_regs = NULL;
> -		state->signal = false;
> +		state->signal = is_kretprobe_trampoline(state->ip);
>  		break;
>  
>  	case UNWIND_HINT_TYPE_REGS:
> -- 
> 2.30.2
> 

-- 
Kees Cook