linux-kernel - Re: [PATCH] powerpc/fsl_book3e: Don't set rodata RO too early

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Message-ID: <20220519182937.GA80472@roeck-us.net>
Date:   Thu, 19 May 2022 11:29:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/fsl_book3e: Don't set rodata RO too early

On Thu, May 19, 2022 at 07:24:15PM +0200, Christophe Leroy wrote:
> On fsl_book3e, rodata is set read-only at the same time as
> init text is set NX at the end of init. That's too early.
> 
> As both action are performed at the same time, delay both
> actions to the time rodata is expected to be made read-only.
> 
> It means we will have a small window with init mem freed but
> still executable. It shouldn't be an issue though, especially
> because the said memory gets poisoned and should therefore
> result to a bad instruction fault in case it gets executer.

executed

> 
> mmu_mark_initmem_nx() is bailing out before doing anything when
> CONFIG_STRICT_KERNEL_RWX is not selected or rodata_enabled is false.
> 
> mmu_mark_rodata_ro() is called only when CONFIG_STRICT_KERNEL_RWX
> is selected and rodata_enabled is true so this is equivalent.
> 
> Move code from mmu_mark_initmem_nx() into mmu_mark_rodata_ro() and
> remove the call to strict_kernel_rwx_enabled() which is not needed
> anymore.
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Fixes: d5970045cf9e ("powerpc/fsl_booke: Update of TLBCAMs after init")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter