linux-kernel - Re: [PATCH v3 02/24] powerpc/secvar: WARN_ON

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Message-Id: <CPVRCZ8Z84K4.337F5K1N7RCRS@bobo>
Date:   Thu, 19 Jan 2023 10:59:12 +1000
From:   "Nicholas Piggin" <npiggin@...il.com>
To:     "Andrew Donnellan" <ajd@...ux.ibm.com>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-integrity@...r.kernel.org>
Cc:     <sudhakar@...ux.ibm.com>, <bgray@...ux.ibm.com>,
        <erichte@...ux.ibm.com>, <gregkh@...uxfoundation.org>,
        <nayna@...ux.ibm.com>, <linux-kernel@...r.kernel.org>,
        <zohar@...ux.ibm.com>, <gjoyce@...ux.ibm.com>,
        <gcwilson@...ux.ibm.com>
Subject: Re: [PATCH v3 02/24] powerpc/secvar: WARN_ON_ONCE() if multiple
 secvar ops are set

On Wed Jan 18, 2023 at 4:10 PM AEST, Andrew Donnellan wrote:
> From: Russell Currey <ruscur@...sell.cc>
>
> The secvar code only supports one consumer at a time.
>
> Multiple consumers aren't possible at this point in time, but we'd want
> it to be obvious if it ever could happen.
>
> Signed-off-by: Russell Currey <ruscur@...sell.cc>
> Signed-off-by: Andrew Donnellan <ajd@...ux.ibm.com>
> ---
>  arch/powerpc/kernel/secvar-ops.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/secvar-ops.c b/arch/powerpc/kernel/secvar-ops.c
> index 6a29777d6a2d..aa1b2adc2710 100644
> --- a/arch/powerpc/kernel/secvar-ops.c
> +++ b/arch/powerpc/kernel/secvar-ops.c
> @@ -8,10 +8,12 @@
>  
>  #include <linux/cache.h>
>  #include <asm/secvar.h>
> +#include <asm/bug.h>
>  
> -const struct secvar_operations *secvar_ops __ro_after_init;
> +const struct secvar_operations *secvar_ops __ro_after_init = NULL;
>  
>  void set_secvar_ops(const struct secvar_operations *ops)
>  {
> +	WARN_ON_ONCE(secvar_ops);
>  	secvar_ops = ops;

You could make it return error here and two line patch in the caller to
handle the error and then things wouldn't get corrupted.

Thanks,
Nick