From: Ard Biesheuvel <ardb@kernel.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Guenter Roeck <linux@roeck-us.net>,
Darren Hart <dvhart@infradead.org>,
Andy Shevchenko <andy@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, linux-efi@vger.kernel.org,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] x86/mm+efi: Avoid creating W+X mappings
Date: Fri, 23 Sep 2022 00:08:57 +0200 [thread overview]
Message-ID: <CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@mail.gmail.com> (raw)
In-Reply-To: <20220922193157.1673623-1-dave.hansen@linux.intel.com>
On Thu, 22 Sept 2022 at 21:32, Dave Hansen <dave.hansen@linux.intel.com> wrote:
>
> From: Peter Zijlstra <peterz@infradead.org>
>
> I'm planning on sticking this in x86/mm so that it goes upstream
> along with the W+X detection code.
>
> --
>
> A recent x86/mm change warns and refuses to create W+X mappings.
>
> The 32-bit EFI code tries to create such a mapping and trips over
> the new W+X refusal.
>
> Make the EFI_RUNTIME_SERVICES_CODE mapping read-only to fix it.
>
This is not safe. EFI_RUNTIME_SERVICES_CODE covers both .text and
.data sections of the EFI runtime PE/COFF executables in memory, so
you are essentially making .data and .bss read-only. (Whether those
executables actually modify their .data and .bss at runtime is a
different matter, but the point is that it used to be possible)
More recent firmwares may provide a 'memory attributes table'
separately which describes the individual sections, but older 32-bit
firmwares are not even built with 4k section alignment, so code and
data may share a single page. Note that we haven't wired up this
memory attributes table on i386 at the moment, and I seriously doubt
that 32-bit firmware in the field exposes it.
Can we just turn off this feature for 32-bit?
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Darren Hart <dvhart@infradead.org>
> Cc: Andy Shevchenko <andy@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: x86@kernel.org
> Cc: linux-efi@vger.kernel.org
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Link: https://lore.kernel.org/all/d8cd7c7e-24c1-7f70-24a9-91c77aa634af@roeck-us.net/
> ---
> arch/x86/platform/efi/efi_32.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c
> index e06a199423c0..d81e379fcd43 100644
> --- a/arch/x86/platform/efi/efi_32.c
> +++ b/arch/x86/platform/efi/efi_32.c
> @@ -136,6 +136,7 @@ void __init efi_runtime_update_mappings(void)
> if (md->type != EFI_RUNTIME_SERVICES_CODE)
> continue;
>
> + set_memory_ro(md->virt_addr, md->num_pages);
> set_memory_x(md->virt_addr, md->num_pages);
> }
> }
next prev parent reply other threads:[~2022-09-22 22:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <08906193-246b-c874-8bac-1d98d2313ac4@roeck-us.net>
2022-09-22 19:31 ` [PATCH] x86/mm+efi: Avoid creating W+X mappings Dave Hansen
2022-09-22 22:08 ` Ard Biesheuvel [this message]
2022-09-23 6:59 ` Peter Zijlstra
2022-09-23 9:49 ` Ard Biesheuvel
2022-09-23 13:58 ` Guenter Roeck
2022-09-23 14:26 ` Ard Biesheuvel
2022-09-23 18:31 ` Kees Cook
2022-09-23 19:53 ` Ard Biesheuvel
2022-09-23 21:19 ` Kees Cook
2022-09-23 22:15 ` Dave Hansen
2022-09-23 22:32 ` Eric W. Biederman
2022-09-24 0:04 ` Kees Cook
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