linux-kernel - Re: [PATCH] static_call: Fix the module key fixup

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Message-ID: <20210225221151.7f9f04d7@oasis.local.home>
Date:   Thu, 25 Feb 2021 22:11:51 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] static_call: Fix the module key fixup

On Thu, 25 Feb 2021 23:03:51 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> Subject: static_call: Fix the module key fixup
> 
> Provided the target address of a R_X86_64_PC32 relocation is aligned,
> the low two bits should be invariant between the relative and absolute
> value.
> 
> Turns out the address is not aligned and things go sideways, ensure we
> transfer the bits in the absolute form when fixing up the key address.
> 

Link: https://lore.kernel.org/lkml/20210225131221.11dab26e@gandalf.local.home/

> Reported-by: Steven Rostedt <rostedt@...dmis.org>

Tested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/static_call.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/static_call.c b/kernel/static_call.c
> index 6906c6ec4c97..ae825295cf68 100644
> --- a/kernel/static_call.c
> +++ b/kernel/static_call.c
> @@ -349,7 +349,8 @@ static int static_call_add_module(struct module *mod)
>  	struct static_call_site *site;
>  
>  	for (site = start; site != stop; site++) {
> -		unsigned long addr = (unsigned long)static_call_key(site);
> +		unsigned long s_key = (long)site->key + (long)&site->key;
> +		unsigned long addr = s_key & ~STATIC_CALL_SITE_FLAGS;
>  		unsigned long key;
>  
>  		/*
> @@ -373,8 +374,8 @@ static int static_call_add_module(struct module *mod)
>  			return -EINVAL;
>  		}
>  
> -		site->key = (key - (long)&site->key) |
> -			    (site->key & STATIC_CALL_SITE_FLAGS);
> +		key |= s_key & STATIC_CALL_SITE_FLAGS;
> +		site->key = key - (long)&site->key;
>  	}
>  
>  	return __static_call_init(mod, start, stop);