Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

[Ingo Molnar]

* Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> On Wed, May 20, 2015 at 12:33:39PM +0200, Ingo Molnar wrote:
> > 
> > * Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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.

Yeah, so many of these seem to be 'leaf only' functions: functions 
that don't ever call functions themselves.

So lets assume we always have CONFIG_FRAME_POINTERS=y.

If they don't set up a frame pointer then they in essence won't show 
up in the call chain - but normally they wouldn't because they call 
nothing.

If they trigger an exception/fault or if they get hit by an interrupt 
then I think we'll still correctly walk the stack - just those 
functions might be missing from the deterministic call chain, right? 
(it will still show up as a '?' entry.)

If they crash then we'll see them because the crashing RIP will be 
printed.

So I'm wondering what the x86 policy here should be: to create frame 
pointers in them or not. Cc:-ed a few more gents for thoughts.

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/