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Message-ID: <CALCETrWAP=7dN8P3dn0JwYTn2SHYtyi-3z7KqGcjV0X6d=s50g@mail.gmail.com> Date: Wed, 20 May 2015 09:03:37 -0700 From: Andy Lutomirski <luto@...capital.net> To: Ingo Molnar <mingo@...nel.org> Cc: Josh Poimboeuf <jpoimboe@...hat.com>, 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 ML <x86@...nel.org>, live-patching@...r.kernel.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Denys Vlasenko <dvlasenk@...hat.com>, Brian Gerst <brgerst@...il.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Borislav Petkov <bp@...en8.de>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation On Wed, May 20, 2015 at 7:48 AM, Ingo Molnar <mingo@...nel.org> wrote: > > * Josh Poimboeuf <jpoimboe@...hat.com> wrote: > >> 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. > > 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.) I've never quite understood what the '?' means. > > 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. > I think it would be nice to have full DWARF unwind support for everything at some point. Unfortunately, I don't see any easy path to getting there. It doesn't help that AFAIK no one has ever proposed a usable in-kernel DWARF unwinder. It also doesn't help that writing correct CFI annotations in inline asm can be very complicated. I think that ia64 manages to have complete unwind support. How did they manage it? If we had an unwinder, it would be relatively straightforward to write something perf-based that would frequently check that we can unwind all the way out of an NMI back to userspace and warn if we couldn't. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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