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From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, Ashok Raj <ashok.raj@intel.com>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>, Peter Anvin <hpa@zytor.com>
Subject: Re: [patch 2/2] x86/boot/32: Disable stackprotector and tracing for mk_early_pgtbl_32()
Date: Thu, 7 Sep 2023 00:17:39 +0200	[thread overview]
Message-ID: <ZPj6gxSUc8SLzpLQ@gmail.com> (raw)
In-Reply-To: <20230822121954.036339203@linutronix.de>


* Thomas Gleixner <tglx@linutronix.de> wrote:

> Stackprotector cannot work before paging is enabled. The read from the per
> CPU variable __stack_chk_guard is always accessing the virtual address
> either directly on UP or via FS on SMP. In physical address mode this
> results in an access to memory above 3GB.
> 
> So this works by chance as the hardware returns the same value when there
> is no RAM at this physical address. When there is RAM populated above 3G
> then the read is by chance the same as nothing changes that memory during
> the very early boot stage.
> 
> Stop relying on pure luck and disable the stack protector for the only C
> function which is called during early boot before paging is enabled.
> 
> Remove function tracing from the whole source file as there is no way to
> trace this at all, but in case of CONFIG_DYNAMIC_FTRACE=n
> mk_early_pgtbl_32() would access global function tracer variables in
> physcial address mode which again might work by chance.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/kernel/Makefile |    1 +
>  arch/x86/kernel/head32.c |    3 ++-
>  2 files changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo

      reply	other threads:[~2023-09-06 22:17 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-22 12:20 [patch 0/2] x86/microcode: Make 32-bit early loading robust and correct Thomas Gleixner
2023-08-22 12:20 ` [patch 1/2] x86/microcode/32: Move early loading after paging enable Thomas Gleixner
2023-08-23 10:16   ` [patch V2 " Thomas Gleixner
2023-09-06 22:17   ` [patch " Ingo Molnar
2023-09-06 22:18     ` Ingo Molnar
2023-08-22 12:20 ` [patch 2/2] x86/boot/32: Disable stackprotector and tracing for mk_early_pgtbl_32() Thomas Gleixner
2023-09-06 22:17   ` Ingo Molnar [this message]

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