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From: Ingo Molnar <mingo@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
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: Fri, 15 Jan 2016 11:56:04 +0100	[thread overview]
Message-ID: <20160115105603.GA25002@gmail.com> (raw)
In-Reply-To: <20160115060652.GA16760@treble.redhat.com>


* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> Some of the 'weird' cases:
> 
> - Some functions use 'ljmp' or 'lret'.  After looking at this some more,
>   I think it would be safe for stacktool to translate the use of these
>   instructions to mean "I know what I'm doing" and just ignore the
>   function.  100% of the functions are safe to ignore anyway.  So we can
>   get rid of those markers and just make stacktool smarter.

Yeah.

So the worry people have is that once such annotations get in, the incentive to 
solve them at the tooling level decreases and stays on a TODO list for a long time 
;-)

> - 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)

Yeah, probably. Annotating Xen special code looks acceptable.

> - The error path in arch/x86/net/bpf_jit.S uses 'leaveq' to do a double
>   return so that it returns from its caller's context.  stacktool
>   doesn't know how to distinguish this from a frame pointer programming
>   bug.  I think the only way to avoid a whitelist marker here would be
>   to rewrite the bpf code to conform with more traditional rbp usage
>   (but I don't know if that would really be a good idea because it would
>   probably result in slower/more code).

I think annotation is fine in this case.

> - __bpf_prog_run() uses a jump table:
> 
>     goto *jumptable[insn->code];
> 
>   stacktool doesn't have an x86 emulator, so it doesn't know how to
>   deterministically follow all possible branches for a dynamic jump.
> 
> - schedule() mucks with the frame pointer which is normally not allowed.

That is obviously a special case too.

As long as no 'usual' C function gets annotated as doing something weird with the 
stack frame, I'm fine with this approach.

Thanks,

	Ingo

  parent reply	other threads:[~2016-01-15 10:56 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
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 [this message]
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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