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Message-ID: <20150520141331.GA16995@treble.redhat.com>
Date:	Wed, 20 May 2015 09:13:31 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

On Wed, May 20, 2015 at 12:33:39PM +0200, Ingo Molnar wrote:
> 
> * Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> > In discussions around the live kernel patching consistency model RFC
> > [1], Peter and Ingo correctly pointed out that stack traces aren't
> > reliable.  And as Ingo said, there's no "strong force" which ensures we
> > can rely on them.
> > 
> > So I've been thinking about how to fix that.  My goal is to eventually
> > make stack traces reliable.  Or at the very least, to be able to detect
> > at runtime when a given stack trace *might* be unreliable.  But improved
> > stack traces would broadly benefit the entire kernel, regardless of the
> > outcome of the live kernel patching consistency model discussions.
> > 
> > This patch set is just the first in a series of proposed stack trace
> > reliability improvements.  Future proposals will include runtime stack
> > reliability checking, as well as compile-time and runtime DWARF
> > validations.
> > 
> > As far as I can tell, there are two main obstacles which prevent frame
> > pointer based stack traces from being reliable:
> > 
> > 1) Missing frame pointer logic: currently, most assembly functions don't
> >    set up the frame pointer.
> 
> Could you please paste here the output of what the new checks print 
> for x86/64 defconfig?

Here are all 89 warnings from defconfig:

arch/x86/ia32/ia32entry.o: ia32_sysenter_target() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/ia32/ia32entry.o: return instruction outside of a function at .entry.text+0x52e.  Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x359.  Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x19be.  Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x19e5.  Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x1c21.  Please use FUNC_ENTER.
arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x1ceb.  Please use FUNC_ENTER.
arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/platform/efi/efi_stub_64.o: efi_call() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x6b.  Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0xc7.  Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x110.  Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x145.  Please use FUNC_ENTER.
arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x1c4.  Please use FUNC_ENTER.
arch/x86/realmode/rm/trampoline_64.o: return instruction outside of a function at .text+0x170.  Please use FUNC_ENTER.
arch/x86/realmode/rm/trampoline_64.o: return instruction outside of a function at .text+0x176.  Please use FUNC_ENTER.
arch/x86/kernel/head_64.o: return instruction outside of a function at .head.text+0x1a2.  Please use FUNC_ENTER.
arch/x86/kernel/head_64.o: start_cpu0() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/kernel/head_64.o: early_idt_handler() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/realmode/rm/reboot.o: return instruction outside of a function at .text+0x2a.  Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: memcpy() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: memset() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: copy_from_fs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/realmode/rm/copy.o: copy_to_fs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/realmode/rm/bioscall.o: intcall() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/int80.o: __kernel_sigreturn() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/int80.o: __kernel_rt_sigreturn() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/int80.o: __kernel_vsyscall() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/syscall.o: __kernel_sigreturn() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/syscall.o: __kernel_rt_sigreturn() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/syscall.o: __kernel_vsyscall() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/sysenter.o: __kernel_sigreturn() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/vdso/vdso32/sysenter.o: __kernel_rt_sigreturn() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/power/hibernate_asm_64.o: return instruction outside of a function at .text+0x69.  Please use FUNC_ENTER.
arch/x86/power/hibernate_asm_64.o: return instruction outside of a function at .text+0x16d.  Please use FUNC_ENTER.
arch/x86/lib/msr-reg.o: rdmsr_safe_regs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/msr-reg.o: wrmsr_safe_regs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/iomap_copy_64.o: __iowrite32_copy() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/clear_page_64.o: clear_page() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/clear_page_64.o: clear_page_orig() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/clear_page_64.o: clear_page_c_e() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/cmpxchg16b_emu.o: this_cpu_cmpxchg16b_emu() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_page_64.o: copy_page() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_page_64.o: copy_page_regs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: _copy_to_user() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: _copy_from_user() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: copy_user_generic_unrolled() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: copy_user_generic_string() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: copy_user_enhanced_fast_string() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: __copy_user_nocache() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/copy_user_64.o: bad_from_user() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/csum-copy_64.o: csum_partial_copy_generic() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_1() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_2() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_4() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/getuser.o: __get_user_8() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/getuser.o: return instruction outside of a function at .text+0xc5.  Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: memcpy() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: __memcpy() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: memcpy_erms() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memcpy_64.o: memcpy_orig() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memmove_64.o: memmove() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memmove_64.o: __memmove() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memmove_64.o: return instruction outside of a function at .altinstr_replacement+0x5.  Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: memset() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: __memset() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: memset_erms() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/memset_64.o: memset_orig() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_1() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_2() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_4() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/putuser.o: __put_user_8() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/putuser.o: return instruction outside of a function at .text+0xc1.  Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_down_read_failed() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_down_write_failed() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_wake() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/lib/rwsem.o: call_rwsem_downgrade_wake() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/bioscall.o: intcall() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/copy.o: memcpy() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/copy.o: memset() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/copy.o: copy_from_fs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/copy.o: copy_to_fs() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/pmjump.o: protected_mode_jump() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/pmjump.o: in_pm32() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/compressed/head_64.o: return instruction outside of a function at .text+0x16e.  Please use FUNC_ENTER.
arch/x86/boot/compressed/head_64.o: return instruction outside of a function at .text+0x172.  Please use FUNC_ENTER.
arch/x86/boot/compressed/head_64.o: startup_32() is missing frame pointer logic.  Please use FUNC_ENTER.
arch/x86/boot/header.o: die() is missing frame pointer logic.  Please use FUNC_ENTER.

> > As a first step, all reported non-compliances result in warnings.  
> > Right now I'm seeing 200+ warnings.  Once we get them all cleaned 
> > up, we can change the warnings to build errors so the asm code can 
> > stay clean.
> 
> That's quite a bit ...

Yeah, a Fedora-based config has over 200 warnings.  Most of the
differences between the above 89 warnings for defconfig and the 200+ for
a Fedora config seem to be caused by xen, crypto and bpf.

-- 
Josh
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