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Message-ID: <20150521205425.GA31662@treble.redhat.com> Date: Thu, 21 May 2015 15:54:25 -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, 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 04:48:10PM +0200, Ingo Molnar wrote: > 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. After removing the frame pointer checks for leaf functions, and adding a check for all functions which jump outside of their scope, the number of defconfig warnings dropped from 89 -> 47. The Fedora config warning count dropped from 207 -> 83. Here are the remaining 47 warnings for defconfig: stackvalidate: arch/x86/ia32/ia32entry.o: ia32_sysenter_target() is missing frame pointer logic stackvalidate: arch/x86/ia32/ia32entry.o: return instruction outside of a function at .entry.text+0x52e stackvalidate: arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x359 stackvalidate: arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x19be stackvalidate: arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x19e5 stackvalidate: arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x1c21 stackvalidate: arch/x86/kernel/entry_64.o: return instruction outside of a function at .entry.text+0x1ceb stackvalidate: arch/x86/kernel/acpi/wakeup_64.o: unsupported jump to outside of the function at wakeup_long64+0x15 stackvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel() is missing frame pointer logic stackvalidate: arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x6b stackvalidate: arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0xc7 stackvalidate: arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x110 stackvalidate: arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x145 stackvalidate: arch/x86/kernel/relocate_kernel_64.o: return instruction outside of a function at .text+0x1c4 stackvalidate: arch/x86/kernel/head_64.o: return instruction outside of a function at .head.text+0x1a2 stackvalidate: arch/x86/kernel/head_64.o: early_idt_handler() is missing frame pointer logic stackvalidate: arch/x86/platform/efi/efi_stub_64.o: efi_call() is missing frame pointer logic stackvalidate: arch/x86/realmode/rm/trampoline_64.o: return instruction outside of a function at .text+0x170 stackvalidate: arch/x86/realmode/rm/trampoline_64.o: return instruction outside of a function at .text+0x176 stackvalidate: arch/x86/realmode/rm/reboot.o: return instruction outside of a function at .text+0x2a stackvalidate: arch/x86/realmode/rm/copy.o: copy_from_fs() is missing frame pointer logic stackvalidate: arch/x86/realmode/rm/copy.o: copy_to_fs() is missing frame pointer logic stackvalidate: arch/x86/power/hibernate_asm_64.o: return instruction outside of a function at .text+0x69 stackvalidate: arch/x86/power/hibernate_asm_64.o: return instruction outside of a function at .text+0x16d stackvalidate: arch/x86/lib/copy_user_64.o: unsupported jump to outside of the function at _copy_to_user+0x25 stackvalidate: arch/x86/lib/copy_user_64.o: unsupported jump to outside of the function at _copy_from_user+0x25 stackvalidate: arch/x86/lib/getuser.o: unsupported jump to outside of the function at __get_user_1+0x14 stackvalidate: arch/x86/lib/getuser.o: unsupported jump to outside of the function at __get_user_2+0x4 stackvalidate: arch/x86/lib/getuser.o: unsupported jump to outside of the function at __get_user_4+0x4 stackvalidate: arch/x86/lib/getuser.o: unsupported jump to outside of the function at __get_user_8+0x4 stackvalidate: arch/x86/lib/getuser.o: return instruction outside of a function at .text+0xc5 stackvalidate: arch/x86/lib/memmove_64.o: return instruction outside of a function at .altinstr_replacement+0x5 stackvalidate: arch/x86/lib/putuser.o: unsupported jump to outside of the function at __put_user_1+0x14 stackvalidate: arch/x86/lib/putuser.o: unsupported jump to outside of the function at __put_user_2+0x1b stackvalidate: arch/x86/lib/putuser.o: unsupported jump to outside of the function at __put_user_4+0x1b stackvalidate: arch/x86/lib/putuser.o: unsupported jump to outside of the function at __put_user_8+0x1b stackvalidate: arch/x86/lib/putuser.o: return instruction outside of a function at .text+0xc1 stackvalidate: arch/x86/lib/rwsem.o: call_rwsem_down_read_failed() is missing frame pointer logic stackvalidate: arch/x86/lib/rwsem.o: call_rwsem_down_write_failed() is missing frame pointer logic stackvalidate: arch/x86/lib/rwsem.o: call_rwsem_wake() is missing frame pointer logic stackvalidate: arch/x86/lib/rwsem.o: call_rwsem_downgrade_wake() is missing frame pointer logic stackvalidate: arch/x86/boot/copy.o: copy_from_fs() is missing frame pointer logic stackvalidate: arch/x86/boot/copy.o: copy_to_fs() is missing frame pointer logic stackvalidate: arch/x86/boot/compressed/head_64.o: return instruction outside of a function at .text+0x16e stackvalidate: arch/x86/boot/compressed/head_64.o: return instruction outside of a function at .text+0x172 stackvalidate: arch/x86/boot/compressed/head_64.o: startup_32() is missing frame pointer logic stackvalidate: arch/x86/boot/pmjump.o: unsupported jump to outside of the function at in_pm32+0x1c Note that only 13 of the 47 warnings are actually due to missing frame pointer logic. The rest are ambiguous conditions which prevent stackvalidate from being able to make sense of things: returning from outside of a proper ELF function, or jumping from inside of a function to outside of its scope. Similarly, in the Fedora config case, only 27 of the 83 warnings are for missing frame pointer logic. If there are no objections, I'll go with this approach in the next version of the patch set. Thanks! -- Josh -- 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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