From: Peter Zijlstra <peterz@infradead.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
Mark Rutland <mark.rutland@arm.com>, X86 ML <x86@kernel.org>,
Kees Cook <keescook@chromium.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-hardening@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
llvm@lists.linux.dev
Subject: Re: [PATCH] static_call,x86: Robustify trampoline patching
Date: Tue, 2 Nov 2021 13:57:44 +0100 [thread overview]
Message-ID: <YYE1yPClPMHvyvIt@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMj1kXGhRmdM3om289Q2-s1Pzfob3D2iSDMorzggfhSk1oj53A@mail.gmail.com>
On Mon, Nov 01, 2021 at 03:14:41PM +0100, Ard Biesheuvel wrote:
> On Mon, 1 Nov 2021 at 10:05, Peter Zijlstra <peterz@infradead.org> wrote:
> > How is that not true for the jump table approach? Like I showed earlier,
> > it is *trivial* to reconstruct the actual function pointer from a
> > jump-table entry pointer.
> >
>
> That is not the point. The point is that Clang instruments every
> indirect call that it emits, to check whether the type of the jump
> table entry it is about to call matches the type of the caller. IOW,
> the indirect calls can only branch into jump tables, and all jump
> table entries in a table each branch to the start of some function of
> the same type.
>
> So the only thing you could achieve by adding or subtracting a
> constant value from the indirect call address is either calling
> another function of the same type (if you are hitting another entry in
> the same table), or failing the CFI type check.
Ah, I see, so the call-site needs to have a branch around the indirect
call instruction.
> Instrumenting the callee only needs something like BTI, and a
> consistent use of the landing pads to ensure that you cannot trivially
> omit the check by landing right after it.
That does bring up another point tho; how are we going to do a kernel
that's optimal for both software CFI and hardware aided CFI?
All questions that need answering I think.
So how insane is something like this, have each function:
foo.cfi:
endbr64
xorl $0xdeadbeef, %r10d
jz foo
ud2
nop # make it 16 bytes
foo:
# actual function text goes here
And for each hash have two thunks:
# arg: r11
# clobbers: r10, r11
__x86_indirect_cfi_deadbeef:
movl -9(%r11), %r10 # immediate in foo.cfi
xorl $0xdeadbeef, %r10 # our immediate
jz 1f
ud2
1: ALTERNATIVE_2 "jmp *%r11",
"jmp __x86_indirect_thunk_r11", X86_FEATURE_RETPOLINE
"lfence; jmp *%r11", X86_FEATURE_RETPOLINE_AMD
# arg: r11
# clobbers: r10, r11
__x86_indirect_ibt_deadbeef:
movl $0xdeadbeef, %r10
subq $0x10, %r11
ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE
jmp *%r11
And have the actual indirect callsite look like:
# r11 - &foo
ALTERNATIVE_2 "cs call __x86_indirect_thunk_r11",
"cs call __x86_indirect_cfi_deadbeef", X86_FEATURE_CFI
"cs call __x86_indirect_ibt_deadbeef", X86_FEATURE_IBT
Although if the compiler were to emit:
cs call __x86_indirect_cfi_deadbeef
we could probaly fix it up from there.
Then we can at runtime decide between:
{!cfi, cfi, ibt} x {!retpoline, retpoline, retpoline-amd}
next prev parent reply other threads:[~2021-11-02 12:58 UTC|newest]
Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-13 18:16 [PATCH v5 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 01/15] objtool: Add CONFIG_CFI_CLANG support Sami Tolvanen
2021-10-13 18:59 ` Kees Cook
2021-10-14 0:44 ` Josh Poimboeuf
2021-10-14 10:22 ` Peter Zijlstra
2021-10-14 19:20 ` Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 02/15] objtool: Add ASM_STACK_FRAME_NON_STANDARD Sami Tolvanen
2021-10-13 18:59 ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 03/15] linkage: Add DECLARE_NOT_CALLED_FROM_C Sami Tolvanen
2021-10-13 19:00 ` Kees Cook
2021-10-15 2:51 ` Andy Lutomirski
2021-10-15 15:35 ` Sami Tolvanen
2021-10-15 15:55 ` Thomas Gleixner
2021-10-15 16:22 ` Andy Lutomirski
2021-10-15 16:47 ` Sami Tolvanen
2021-10-15 17:34 ` Andy Lutomirski
2021-10-15 17:57 ` Thomas Gleixner
2021-10-15 18:42 ` Sami Tolvanen
2021-10-15 19:35 ` Andy Lutomirski
2021-10-15 20:37 ` Sami Tolvanen
2021-10-16 21:12 ` Josh Poimboeuf
2021-10-18 17:08 ` Sami Tolvanen
2021-10-15 22:17 ` Thomas Gleixner
2021-10-16 21:16 ` Josh Poimboeuf
2021-10-13 18:16 ` [PATCH v5 04/15] cfi: Add DEFINE_CFI_IMMEDIATE_RETURN_STUB Sami Tolvanen
2021-10-13 19:02 ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 05/15] tracepoint: Exclude tp_stub_func from CFI checking Sami Tolvanen
2021-10-13 19:03 ` Kees Cook
2021-10-13 19:20 ` Steven Rostedt
2021-10-13 18:16 ` [PATCH v5 06/15] ftrace: Use an opaque type for functions not callable from C Sami Tolvanen
2021-10-13 19:04 ` Kees Cook
2021-10-13 19:20 ` Steven Rostedt
2021-10-13 18:16 ` [PATCH v5 07/15] lkdtm: Disable UNSET_SMEP with CFI Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 08/15] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 09/15] x86: Use an opaque type for functions not callable from C Sami Tolvanen
2021-10-14 11:21 ` Borislav Petkov
2021-10-14 16:07 ` Kees Cook
2021-10-14 17:31 ` Borislav Petkov
2021-10-14 18:24 ` Sami Tolvanen
2021-10-14 19:00 ` Nick Desaulniers
2021-10-14 18:47 ` Kees Cook
2021-10-14 18:52 ` Steven Rostedt
2021-10-14 19:06 ` Josh Poimboeuf
2021-10-13 18:16 ` [PATCH v5 10/15] x86/purgatory: Disable CFI Sami Tolvanen
2021-10-13 19:05 ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 11/15] x86, relocs: Ignore __typeid__ relocations Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 12/15] x86, module: " Sami Tolvanen
2021-10-13 18:55 ` Kees Cook
2021-10-13 18:16 ` [PATCH v5 13/15] x86, cpu: Use LTO for cpu.c with CFI Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 14/15] x86, kprobes: Fix optprobe_template_func type mismatch Sami Tolvanen
2021-10-13 18:16 ` [PATCH v5 15/15] x86, build: Allow CONFIG_CFI_CLANG to be selected Sami Tolvanen
2021-10-13 18:56 ` Kees Cook
2021-10-13 19:07 ` [PATCH v5 00/15] x86: Add support for Clang CFI Kees Cook
2021-10-19 10:06 ` Alexander Lobakin
2021-10-19 15:40 ` Sami Tolvanen
2021-10-21 10:27 ` Alexander Lobakin
2021-10-26 20:16 ` Peter Zijlstra
2021-10-27 10:02 ` David Laight
2021-10-27 10:17 ` Peter Zijlstra
2021-10-27 12:05 ` Mark Rutland
2021-10-27 12:22 ` Ard Biesheuvel
2021-10-27 12:48 ` Peter Zijlstra
2021-10-27 13:04 ` Peter Zijlstra
2021-10-27 13:30 ` Ard Biesheuvel
2021-10-27 14:03 ` Peter Zijlstra
2021-10-27 14:18 ` Ard Biesheuvel
2021-10-27 14:36 ` Peter Zijlstra
2021-10-27 15:50 ` Sami Tolvanen
2021-10-27 15:55 ` Ard Biesheuvel
2021-10-29 20:03 ` Peter Zijlstra
2021-10-30 7:47 ` [PATCH] static_call,x86: Robustify trampoline patching Peter Zijlstra
2021-10-30 8:16 ` Peter Zijlstra
2021-11-02 17:35 ` Kees Cook
2021-11-02 18:15 ` Peter Zijlstra
2021-11-15 13:09 ` Rasmus Villemoes
2021-10-30 17:19 ` Ard Biesheuvel
2021-10-30 18:02 ` Peter Zijlstra
2021-10-30 18:55 ` Ard Biesheuvel
2021-10-31 16:24 ` Ard Biesheuvel
2021-10-31 16:39 ` Peter Zijlstra
2021-10-31 16:44 ` Ard Biesheuvel
2021-10-31 20:09 ` Peter Zijlstra
2021-10-31 20:21 ` Ard Biesheuvel
2021-10-31 20:44 ` Peter Zijlstra
2021-10-31 23:36 ` Ard Biesheuvel
2021-11-01 9:01 ` Peter Zijlstra
2021-11-01 9:36 ` David Laight
2021-11-01 14:14 ` Ard Biesheuvel
2021-11-02 12:57 ` Peter Zijlstra [this message]
2021-11-02 15:15 ` Peter Zijlstra
2021-11-02 17:44 ` Ard Biesheuvel
2021-11-02 18:14 ` Peter Zijlstra
2021-11-02 18:17 ` Peter Zijlstra
2021-11-02 18:18 ` Ard Biesheuvel
2021-11-02 21:48 ` Peter Zijlstra
2021-11-02 18:10 ` Kees Cook
2021-11-02 21:02 ` Andy Lutomirski
2021-11-02 23:13 ` Kees Cook
2021-11-03 0:20 ` Andy Lutomirski
2021-11-03 8:35 ` Peter Zijlstra
2021-11-03 10:01 ` David Laight
2021-11-03 19:32 ` Andy Lutomirski
2021-11-02 21:19 ` Peter Zijlstra
2021-11-11 12:15 ` [tip: locking/urgent] " tip-bot2 for Peter Zijlstra
2021-10-30 19:07 ` [PATCH v5 00/15] x86: Add support for Clang CFI Sami Tolvanen
2021-10-27 17:11 ` Kees Cook
2021-10-27 21:21 ` Peter Zijlstra
2021-10-27 22:27 ` Kees Cook
2021-10-28 11:09 ` Peter Zijlstra
2021-10-28 17:12 ` Kees Cook
2021-10-28 20:29 ` Peter Zijlstra
2021-11-02 17:26 ` Kees Cook
2021-11-01 4:13 ` Andy Lutomirski
2021-10-27 12:46 ` Peter Zijlstra
2021-10-27 12:55 ` David Laight
2021-10-27 13:17 ` Mark Rutland
2021-10-27 21:31 ` David Laight
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