linux-kernel - Re: [PATCH] powerpc/lib: fix book3s/32 boot failure due to code patching

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Date:   Wed, 15 May 2019 08:41:38 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Greg KH <gregkh@...uxfoundation.org>, erhard_f@...lbox.org,
        Michael Neuling <mikey@...ling.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] powerpc/lib: fix book3s/32 boot failure due to code
 patching

Oops, forgot to tell it's for 4.9. Resending with proper subject.

Le 15/05/2019 à 08:39, Christophe Leroy a écrit :
> [Backport of upstream commit b45ba4a51cde29b2939365ef0c07ad34c8321789]
> 
> On powerpc32, patch_instruction() is called by apply_feature_fixups()
> which is called from early_init()
> 
> There is the following note in front of early_init():
>   * Note that the kernel may be running at an address which is different
>   * from the address that it was linked at, so we must use RELOC/PTRRELOC
>   * to access static data (including strings).  -- paulus
> 
> Therefore init_mem_is_free must be accessed with PTRRELOC()
> 
> Fixes: 1c38a84d4586 ("powerpc: Avoid code patching freed init sections")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=203597
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> 
> ---
> Can't apply the upstream commit as such due to several other unrelated stuff
> like for instance STRICT_KERNEL_RWX which are missing.
> So instead, using same approach as for commit 252eb55816a6f69ef9464cad303cdb3326cdc61d
> ---
>   arch/powerpc/lib/code-patching.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index 14535ad4cdd1..c312955977ce 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -23,7 +23,7 @@ int patch_instruction(unsigned int *addr, unsigned int instr)
>   	int err;
>   
>   	/* Make sure we aren't patching a freed init section */
> -	if (init_mem_is_free && init_section_contains(addr, 4)) {
> +	if (*PTRRELOC(&init_mem_is_free) && init_section_contains(addr, 4)) {
>   		pr_debug("Skipping init section patching addr: 0x%px\n", addr);
>   		return 0;
>   	}
>