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* x86/extable: Introduce _ASM_EXTABLE_UA for uaccess fixupsJann Horn2018-09-031-2/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, most fixups for attempting to access userspace memory are handled using _ASM_EXTABLE, which is also used for various other types of fixups (e.g. safe MSR access, IRET failures, and a bunch of other things). In order to make it possible to add special safety checks to uaccess fixups (in particular, checking whether the fault address is actually in userspace), introduce a new exception table handler ex_handler_uaccess() and wire it up to all the user access fixups (excluding ones that already use _ASM_EXTABLE_EX). Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: kernel-hardening@lists.openwall.com Cc: dvyukov@google.com Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Cc: Borislav Petkov <bp@alien8.de> Link: https://lkml.kernel.org/r/20180828201421.157735-5-jannh@google.com
* x86/asm: Don't use RBP as a temporary register in csum_partial_copy_generic()Josh Poimboeuf2017-05-051-6/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Andrey Konovalov reported the following warning while fuzzing the kernel with syzkaller: WARNING: kernel stack regs at ffff8800686869f8 in a.out:4933 has bad 'bp' value c3fc855a10167ec0 The unwinder dump revealed that RBP had a bad value when an interrupt occurred in csum_partial_copy_generic(). That function saves RBP on the stack and then overwrites it, using it as a scratch register. That's problematic because it breaks stack traces if an interrupt occurs in the middle of the function. Replace the usage of RBP with another callee-saved register (R15) so stack traces are no longer affected. Reported-by: Andrey Konovalov <andreyknvl@google.com> Tested-by: Andrey Konovalov <andreyknvl@google.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Cong Wang <xiyou.wangcong@gmail.com> Cc: David S . Miller <davem@davemloft.net> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Kostya Serebryany <kcc@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> Cc: Neil Horman <nhorman@tuxdriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlad Yasevich <vyasevich@gmail.com> Cc: linux-sctp@vger.kernel.org Cc: netdev <netdev@vger.kernel.org> Cc: syzkaller <syzkaller@googlegroups.com> Link: http://lkml.kernel.org/r/4b03a961efda5ec9bfe46b7b9c9ad72d1efad343.1493909486.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* x86/debug: Remove perpetually broken, unmaintainable dwarf annotationsIngo Molnar2015-06-021-17/+0Star
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | So the dwarf2 annotations in low level assembly code have become an increasing hindrance: unreadable, messy macros mixed into some of the most security sensitive code paths of the Linux kernel. These debug info annotations don't even buy the upstream kernel anything: dwarf driven stack unwinding has caused problems in the past so it's out of tree, and the upstream kernel only uses the much more robust framepointers based stack unwinding method. In addition to that there's a steady, slow bitrot going on with these annotations, requiring frequent fixups. There's no tooling and no functionality upstream that keeps it correct. So burn down the sick forest, allowing new, healthier growth: 27 files changed, 350 insertions(+), 1101 deletions(-) Someone who has the willingness and time to do this properly can attempt to reintroduce dwarf debuginfo in x86 assembly code plus dwarf unwinding from first principles, with the following conditions: - it should be maximally readable, and maximally low-key to 'ordinary' code reading and maintenance. - find a build time method to insert dwarf annotations automatically in the most common cases, for pop/push instructions that manipulate the stack pointer. This could be done for example via a preprocessing step that just looks for common patterns - plus special annotations for the few cases where we want to depart from the default. We have hundreds of CFI annotations, so automating most of that makes sense. - it should come with build tooling checks that ensure that CFI annotations are sensible. We've seen such efforts from the framepointer side, and there's no reason it couldn't be done on the dwarf side. Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Frédéric Weisbecker <fweisbec@gmail.com Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jan Beulich <JBeulich@suse.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* x86/asm: Optimize unnecessarily wide TEST instructionsDenys Vlasenko2015-03-071-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | By the nature of the TEST operation, it is often possible to test a narrower part of the operand: "testl $3, mem" -> "testb $3, mem", "testq $3, %rcx" -> "testb $3, %cl" This results in shorter instructions, because the TEST instruction has no sign-entending byte-immediate forms unlike other ALU ops. Note that this change does not create any LCP (Length-Changing Prefix) stalls, which happen when adding a 0x66 prefix, which happens when 16-bit immediates are used, which changes such TEST instructions: [test_opcode] [modrm] [imm32] to: [0x66] [test_opcode] [modrm] [imm16] where [imm16] has a *different length* now: 2 bytes instead of 4. This confuses the decoder and slows down execution. REX prefixes were carefully designed to almost never hit this case: adding REX prefix does not change instruction length except MOVABS and MOV [addr],RAX instruction. This patch does not add instructions which would use a 0x66 prefix, code changes in assembly are: -48 f7 07 01 00 00 00 testq $0x1,(%rdi) +f6 07 01 testb $0x1,(%rdi) -48 f7 c1 01 00 00 00 test $0x1,%rcx +f6 c1 01 test $0x1,%cl -48 f7 c1 02 00 00 00 test $0x2,%rcx +f6 c1 02 test $0x2,%cl -41 f7 c2 01 00 00 00 test $0x1,%r10d +41 f6 c2 01 test $0x1,%r10b -48 f7 c1 04 00 00 00 test $0x4,%rcx +f6 c1 04 test $0x4,%cl -48 f7 c1 08 00 00 00 test $0x8,%rcx +f6 c1 08 test $0x8,%cl Linus further notes: "There are no stalls from using 8-bit instruction forms. Now, changing from 64-bit or 32-bit 'test' instructions to 8-bit ones *could* cause problems if it ends up having forwarding issues, so that instead of just forwarding the result, you end up having to wait for it to be stable in the L1 cache (or possibly the register file). The forwarding from the store buffer is simplest and most reliable if the read is done at the exact same address and the exact same size as the write that gets forwarded. But that's true only if: (a) the write was very recent and is still in the write queue. I'm not sure that's the case here anyway. (b) on at least most Intel microarchitectures, you have to test a different byte than the lowest one (so forwarding a 64-bit write to a 8-bit read ends up working fine, as long as the 8-bit read is of the low 8 bits of the written data). A very similar issue *might* show up for registers too, not just memory writes, if you use 'testb' with a high-byte register (where instead of forwarding the value from the original producer it needs to go through the register file and then shifted). But it's mainly a problem for store buffers. But afaik, the way Denys changed the test instructions, neither of the above issues should be true. The real problem for store buffer forwarding tends to be "write 8 bits, read 32 bits". That can be really surprisingly expensive, because the read ends up having to wait until the write has hit the cacheline, and we might talk tens of cycles of latency here. But "write 32 bits, read the low 8 bits" *should* be fast on pretty much all x86 chips, afaik." Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> Acked-by: Andy Lutomirski <luto@amacapital.net> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: H. Peter Anvin <hpa@linux.intel.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Kees Cook <keescook@chromium.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Will Drewry <wad@chromium.org> Link: http://lkml.kernel.org/r/1425675332-31576-1-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* x86, extable: Remove open-coded exception table entries in ↵H. Peter Anvin2012-04-201-12/+4Star
| | | | | | | | | | | | arch/x86/lib/csum-copy_64.S Remove open-coded exception table entries in arch/x86/lib/csum-copy_64.S, and replace them with _ASM_EXTABLE() macros; this will allow us to change the format and type of the exception table entries. Signed-off-by: H. Peter Anvin <hpa@zytor.com> Cc: David Daney <david.daney@cavium.com> Link: http://lkml.kernel.org/r/CA%2B55aFyijf43qSu3N9nWHEBwaGbb7T2Oq9A=9EyR=Jtyqfq_cQ@mail.gmail.com
* x86: Clean up csum-copy_64.S a bitIngo Molnar2011-03-181-120/+120
| | | | | | | | | The many stray whitespaces and other uncleanlinesses made this code almost unreadable to me - so fix those. No changes to the code. Signed-off-by: Ingo Molnar <mingo@elte.hu>
* x86: Fix common misspellingsLucas De Marchi2011-03-181-2/+2
| | | | | | | | | They were generated by 'codespell' and then manually reviewed. Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi> Cc: trivial@kernel.org LKML-Reference: <1300389856-1099-3-git-send-email-lucas.demarchi@profusion.mobi> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* x86_64: move libThomas Gleixner2007-10-111-0/+249
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>