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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>,
	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: Tue, 19 Jan 2016 23:42:56 -0600	[thread overview]
Message-ID: <20160120054256.GA31495@treble.redhat.com> (raw)
In-Reply-To: <20160115110000.GB25002@gmail.com>

On Fri, Jan 15, 2016 at 12:00:00PM +0100, Ingo Molnar wrote:
> 
> * 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'.)

I've now gotten the number of warnings down to 0 (except for a few
staging drivers), even with allyesconfig (with !CONFIG_GCOV).

I've also managed to make stacktool a little smarter such that the
in-code STACKTOOL_IGNORE_INSN markers are no longer needed, woot!

There's still a need for 4 STACKTOOL_IGNORE_FUNC(name) markers in the
entire tree, due to the weird cases I mentioned.  But they're placed
after the functions, so they're much less disruptive.

I'll be posting a v16 soon.

-- 
Josh

  parent reply	other threads:[~2016-01-20  5:43 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
2016-01-15 11:11               ` Borislav Petkov
2016-01-15 11:13                 ` Ingo Molnar
2016-01-20  5:42               ` Josh Poimboeuf [this message]
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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