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Message-ID: <20170508225308.a6uznrhdm7pgyhcg@treble>
Date: Mon, 8 May 2017 17:53:08 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: Kees Cook <keescook@...omium.org>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
PaX Team <pageexec@...email.hu>, Jann Horn <jannh@...gle.com>,
Eric Biggers <ebiggers3@...il.com>,
Christoph Hellwig <hch@...radead.org>,
"axboe@...nel.dk" <axboe@...nel.dk>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Elena Reshetova <elena.reshetova@...el.com>,
Hans Liljestrand <ishkamiel@...il.com>,
David Windsor <dwindsor@...il.com>,
"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"David S. Miller" <davem@...emloft.net>,
Rik van Riel <riel@...hat.com>,
linux-arch <linux-arch@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 2/2] x86/refcount: Implement fast refcount overflow
protection
On Mon, May 08, 2017 at 12:32:52PM -0700, Kees Cook wrote:
> +#define REFCOUNT_EXCEPTION \
> + "movl $0x7fffffff, %[counter]\n\t" \
> + "int $"__stringify(X86_REFCOUNT_VECTOR)"\n" \
> + "0:\n\t" \
> + _ASM_EXTABLE(0b, 0b)
Despite the objtool warnings going away, this still uses the exception
table in a new way, which will confuse objtool. I need to do some more
thinking about the best way to fix it, either as a change to your patch
or a change to objtool.
> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> index 532372c6cf15..0590f384f234 100644
> --- a/include/asm-generic/sections.h
> +++ b/include/asm-generic/sections.h
> @@ -20,6 +20,8 @@
> * may be out of this range on some architectures.
> * [_sinittext, _einittext]: contains .init.text.* sections
> * [__bss_start, __bss_stop]: contains BSS sections
> + * [__refcount_overflow/underflow_start, ..._end]: contains .text sections
> + * for refcount error handling.
> *
> * Following global variables are optional and may be unavailable on some
> * architectures and/or kernel configurations.
> @@ -39,6 +41,8 @@ extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
> extern char __kprobes_text_start[], __kprobes_text_end[];
> extern char __entry_text_start[], __entry_text_end[];
> extern char __start_rodata[], __end_rodata[];
> +extern char __refcount_overflow_start[], __refcount_overflow_end[];
> +extern char __refcount_underflow_start[], __refcount_underflow_end[];
I think this part is no longer needed, since you got rid of the new
sections?
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 3558f4eb1a86..2f2f34942689 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -446,9 +446,18 @@
> ALIGN_FUNCTION(); \
> *(.text.hot .text .text.fixup .text.unlikely) \
> *(.ref.text) \
> + REFCOUNT_TEXT \
> MEM_KEEP(init.text) \
> MEM_KEEP(exit.text) \
>
> +#define __REFCOUNT_TEXT(section) \
> + VMLINUX_SYMBOL(__##section##_start) = .; \
> + *(.text.##section) \
> + VMLINUX_SYMBOL(__##section##_end) = .;
> +
> +#define REFCOUNT_TEXT \
> + __REFCOUNT_TEXT(refcount_overflow) \
> + __REFCOUNT_TEXT(refcount_underflow)
Same here.
--
Josh
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