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From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	live-patching@vger.kernel.org, Michal Marek <mmarek@suse.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andi Kleen <andi@firstfloor.org>, Pedro Alves <palves@redhat.com>,
	Namhyung Kim <namhyung@gmail.com>,
	Bernd Petrovitsch <bernd@petrovitsch.priv.at>,
	Chris J Arges <chris.j.arges@canonical.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jiri Slaby <jslaby@suse.cz>,
	Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH v15 13/25] x86/reboot: Add ljmp instructions to stacktool whitelist
Date: Fri, 15 Jan 2016 12:00:00 +0100	[thread overview]
Message-ID: <20160115110000.GB25002@gmail.com> (raw)
In-Reply-To: <20160115104145.GC25104@pd.tnic>


* Borislav Petkov <bp@alien8.de> wrote:

> On Fri, Jan 15, 2016 at 12:06:52AM -0600, Josh Poimboeuf wrote:
> > - xen_cpuid() uses some custom xen instructions which start with
> >   XEN_EMULATE_PREFIX.  It corresponds to the following x86 instructions:
> > 
> >     ffffffff8107e572:       0f 0b                   ud2
> >     ffffffff8107e574:       78 65                   js ffffffff8107e5db <xen_get_debugreg+0xa>
> >     ffffffff8107e576:       6e                      outsb %ds:(%rsi),(%dx)
> > 
> >   Apparently(?) xen treats the ud2 special when it's followed by "78 65
> >   6e".  This is confusing for stacktool because ud2 is normally a dead
> >   end, and it thinks the instructions after it will never run.
> >   
> >   (In theory stacktool could be taught to understand this hack, but
> >   that's a bad idea IMO)
> 
> Why, because it is not generic enough?
> 
> Well, you could add a cmdline option "--kernel" which is supplied when
> checking the kernel and such kernel "idiosyncrasies" are handled only
> then and there. And since the tool is part of the kernel, changes to
> XEN_EMULATE_PREFIX, will have to be updated in stacktool too...

So I think because we are talking about less than a dozen annotations, these are 
technicalities - and it might in fact be better to have a single line of obvious 
annotation in a function that does something weird (and arguably all of these 
functions do something weird), than having dozens of lines of code on the tooling 
side to avoid that single line on the kernel side.

That has a documentation value as well.

As long as the annotation itself is not stacktool specific, it should serve as 
documentation as well - such as:

  __non_standard_stack_frame

or:

  __non_C_instructions

?

All of the cases Josh listed involve some sort of special case where we do 
something non-standard. (Where 'standard' == 'regular kernel C function'.)

Thanks,

	Ingo

  reply	other threads:[~2016-01-15 11:00 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-18 12:39 [PATCH v15 00/25] Compile-time stack metadata validation Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 01/25] tools: Fix formatting of the "make -C tools" help message Josh Poimboeuf
2016-01-13  9:40   ` [tip:perf/urgent] " tip-bot for Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 02/25] tools: Make list.h self-sufficient Josh Poimboeuf
2016-01-12 12:35   ` Borislav Petkov
2016-01-12 14:54     ` Arnaldo Carvalho de Melo
2016-01-12 15:59       ` Borislav Petkov
2016-01-12 17:16         ` Arnaldo Carvalho de Melo
2016-01-13  9:40   ` [tip:perf/urgent] " tip-bot for Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 03/25] tools subcmd: Add missing NORETURN define for parse-options.h Josh Poimboeuf
2016-01-13  9:41   ` [tip:perf/urgent] " tip-bot for Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 04/25] x86/asm: Frame pointer macro cleanup Josh Poimboeuf
2016-01-19 13:39   ` [tip:x86/asm] x86/asm: Clean up frame pointer macros tip-bot for Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 05/25] x86/asm: Add C versions of " Josh Poimboeuf
2016-01-19 13:40   ` [tip:x86/asm] " tip-bot for Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 06/25] x86/stacktool: Compile-time stack metadata validation Josh Poimboeuf
2016-01-12 14:48   ` Borislav Petkov
2016-01-12 15:06     ` Josh Poimboeuf
2016-01-12 16:10       ` Borislav Petkov
2016-01-19 12:02   ` Ingo Molnar
2015-12-18 12:39 ` [PATCH v15 07/25] x86/stacktool: Add file and directory ignores Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 08/25] x86/stacktool: Add ignore macros Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 09/25] x86/xen: Add stack frame dependency to hypercall inline asm calls Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 10/25] x86/paravirt: Add stack frame dependency to PVOP " Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 11/25] x86/paravirt: Create a stack frame in PV_CALLEE_SAVE_REGS_THUNK Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 12/25] x86/amd: Set ELF function type for vide() Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 13/25] x86/reboot: Add ljmp instructions to stacktool whitelist Josh Poimboeuf
2016-01-12 16:47   ` Borislav Petkov
2016-01-12 17:43     ` Josh Poimboeuf
2016-01-12 17:55       ` Borislav Petkov
2016-01-12 18:56         ` Josh Poimboeuf
2016-01-12 19:37           ` Borislav Petkov
2016-01-13 10:55       ` Ingo Molnar
2016-01-15  6:06         ` Josh Poimboeuf
2016-01-15 10:41           ` Borislav Petkov
2016-01-15 11:00             ` Ingo Molnar [this message]
2016-01-15 11:11               ` Borislav Petkov
2016-01-15 11:13                 ` Ingo Molnar
2016-01-20  5:42               ` Josh Poimboeuf
2016-01-20  5:50                 ` H. Peter Anvin
2016-01-20  6:09                   ` Josh Poimboeuf
2016-01-20 10:44                 ` Borislav Petkov
2016-01-15 10:56           ` Ingo Molnar
2015-12-18 12:39 ` [PATCH v15 14/25] x86/xen: Add xen_cpuid() and xen_setup_gdt() to stacktool whitelists Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 15/25] x86/asm/crypto: Create stack frames in aesni-intel_asm.S Josh Poimboeuf
2016-01-12 16:53   ` Borislav Petkov
2016-01-12 16:54     ` Borislav Petkov
2015-12-18 12:39 ` [PATCH v15 16/25] x86/asm/crypto: Move .Lbswap_mask data to .rodata section Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 17/25] x86/asm/crypto: Move jump_table " Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 18/25] x86/asm/crypto: Create stack frames in clmul_ghash_mul/update() Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 19/25] x86/asm/entry: Create stack frames in thunk functions Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 20/25] x86/asm/acpi: Create a stack frame in do_suspend_lowlevel() Josh Poimboeuf
2015-12-20 16:13   ` Rafael J. Wysocki
2015-12-18 12:39 ` [PATCH v15 21/25] x86/asm: Create stack frames in rwsem functions Josh Poimboeuf
2016-01-12 12:41   ` Borislav Petkov
2016-01-12 14:36     ` Josh Poimboeuf
2016-01-12 14:40       ` Borislav Petkov
2015-12-18 12:39 ` [PATCH v15 22/25] x86/asm/efi: Create a stack frame in efi_call() Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 23/25] x86/asm/power: Create stack frames in hibernate_asm_64.S Josh Poimboeuf
2015-12-20 16:14   ` Rafael J. Wysocki
2015-12-18 12:39 ` [PATCH v15 24/25] x86/uaccess: Add stack frame output operand in get_user inline asm Josh Poimboeuf
2015-12-18 12:39 ` [PATCH v15 25/25] x86/stacktool: Ignore head_$(BITS) files Josh Poimboeuf
2016-01-12 14:58 ` [PATCH v15 00/25] Compile-time stack metadata validation Arnaldo Carvalho de Melo
2016-01-12 17:17 ` Borislav Petkov
2016-01-12 17:50   ` Josh Poimboeuf
2016-01-12 18:04     ` Borislav Petkov
2016-01-13 10:18   ` Ingo Molnar

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