summaryrefslogtreecommitdiff
path: root/arch/x86/include/asm/cfi.h
AgeCommit message (Collapse)Author
3 dayscfi: Move BPF CFI types and helpers to generic codeSami Tolvanen
Instead of duplicating the same code for each architecture, move the CFI type hash variables for BPF function types and related helper functions to generic CFI code, and allow architectures to override the function definitions if needed. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Link: https://lore.kernel.org/r/20250801001004.1859976-7-samitolvanen@google.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2025-03-03x86/ibt: Make cfi_bhi a constant for FINEIBT_BHI=nPeter Zijlstra
Robot yielded a .config that tripped: vmlinux.o: warning: objtool: do_jit+0x276: relocation to !ENDBR: .noinstr.text+0x6a60 This is the result of using __bhi_args[1] in unreachable code; make sure the compiler is able to determine this is unreachable and trigger DCE. Closes: https://lore.kernel.org/oe-kbuild-all/202503030704.H9KFysNS-lkp@intel.com/ Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20250303094911.GL5880@noisy.programming.kicks-ass.net
2025-02-26x86/ibt: Implement FineIBT-BHI mitigationPeter Zijlstra
While WAIT_FOR_ENDBR is specified to be a full speculation stop; it has been shown that some implementations are 'leaky' to such an extend that speculation can escape even the FineIBT preamble. To deal with this, add additional hardening to the FineIBT preamble. Notably, using a new LLVM feature: https://github.com/llvm/llvm-project/commit/e223485c9b38a5579991b8cebb6a200153eee245 which encodes the number of arguments in the kCFI preamble's register. Using this register<->arity mapping, have the FineIBT preamble CALL into a stub clobbering the relevant argument registers in the speculative case. Scott sayeth thusly: Microarchitectural attacks such as Branch History Injection (BHI) and Intra-mode Branch Target Injection (IMBTI) [1] can cause an indirect call to mispredict to an adversary-influenced target within the same hardware domain (e.g., within the kernel). Instructions at the mispredicted target may execute speculatively and potentially expose kernel data (e.g., to a user-mode adversary) through a microarchitectural covert channel such as CPU cache state. CET-IBT [2] is a coarse-grained control-flow integrity (CFI) ISA extension that enforces that each indirect call (or indirect jump) must land on an ENDBR (end branch) instruction, even speculatively*. FineIBT is a software technique that refines CET-IBT by associating each function type with a 32-bit hash and enforcing (at the callee) that the hash of the caller's function pointer type matches the hash of the callee's function type. However, recent research [3] has demonstrated that the conditional branch that enforces FineIBT's hash check can be coerced to mispredict, potentially allowing an adversary to speculatively bypass the hash check: __cfi_foo: ENDBR64 SUB R10d, 0x01234567 JZ foo # Even if the hash check fails and ZF=0, this branch could still mispredict as taken UD2 foo: ... The techniques demonstrated in [3] require the attacker to be able to control the contents of at least one live register at the mispredicted target. Therefore, this patch set introduces a sequence of CMOV instructions at each indirect-callable target that poisons every live register with data that the attacker cannot control whenever the FineIBT hash check fails, thus mitigating any potential attack. The security provided by this scheme has been discussed in detail on an earlier thread [4]. [1] https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/branch-history-injection.html [2] Intel Software Developer's Manual, Volume 1, Chapter 18 [3] https://www.vusec.net/projects/native-bhi/ [4] https://lore.kernel.org/lkml/20240927194925.707462984@infradead.org/ *There are some caveats for certain processors, see [1] for more info Suggested-by: Scott Constable <scott.d.constable@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Kees Cook <kees@kernel.org> Link: https://lore.kernel.org/r/20250224124200.820402212@infradead.org
2025-02-26x86/bhi: Add BHI stubsPeter Zijlstra
Add an array of code thunks, to be called from the FineIBT preamble, clobbering the first 'n' argument registers for speculative execution. Notably the 0th entry will clobber no argument registers and will never be used, it exists so the array can be naturally indexed, while the 7th entry will clobber all the 6 argument registers and also RSP in order to mess up stack based arguments. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Kees Cook <kees@kernel.org> Link: https://lore.kernel.org/r/20250224124200.717378681@infradead.org
2025-02-14x86/ibt: Handle FineIBT in handle_cfi_failure()Peter Zijlstra
Sami reminded me that FineIBT failure does not hook into the regular CFI failure case, and as such CFI_PERMISSIVE does not work. Reported-by: Sami Tolvanen <samitolvanen@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Link: https://lkml.kernel.org/r/20250214092619.GB21726@noisy.programming.kicks-ass.net
2024-06-19x86/alternatives: Make FineIBT mode Kconfig selectableKees Cook
Since FineIBT performs checking at the destination, it is weaker against attacks that can construct arbitrary executable memory contents. As such, some system builders want to run with FineIBT disabled by default. Allow the "cfi=kcfi" boot param mode to be selectable through Kconfig via the newly introduced CONFIG_CFI_AUTO_DEFAULT. Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Link: https://lore.kernel.org/r/20240501000218.work.998-kees@kernel.org Signed-off-by: Kees Cook <kees@kernel.org>
2023-12-15cfi: Add CFI_NOSEAL()Peter Zijlstra
Add a CFI_NOSEAL() helper to mark functions that need to retain their CFI information, despite not otherwise leaking their address. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20231215092707.669401084@infradead.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2023-12-15x86/cfi,bpf: Fix bpf_struct_ops CFIPeter Zijlstra
BPF struct_ops uses __arch_prepare_bpf_trampoline() to write trampolines for indirect function calls. These tramplines much have matching CFI. In order to obtain the correct CFI hash for the various methods, add a matching structure that contains stub functions, the compiler will generate correct CFI which we can pilfer for the trampolines. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20231215092707.566977112@infradead.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2023-12-15x86/cfi,bpf: Fix bpf_callback_t CFIPeter Zijlstra
Where the main BPF program is expected to match bpf_func_t, sub-programs are expected to match bpf_callback_t. This fixes things like: tools/testing/selftests/bpf/progs/bloom_filter_bench.c: bpf_for_each_map_elem(&array_map, bloom_callback, &data, 0); Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20231215092707.451956710@infradead.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2023-12-15x86/cfi,bpf: Fix BPF JIT callPeter Zijlstra
The current BPF call convention is __nocfi, except when it calls !JIT things, then it calls regular C functions. It so happens that with FineIBT the __nocfi and C calling conventions are incompatible. Specifically __nocfi will call at func+0, while FineIBT will have endbr-poison there, which is not a valid indirect target. Causing #CP. Notably this only triggers on IBT enabled hardware, which is probably why this hasn't been reported (also, most people will have JIT on anyway). Implement proper CFI prologues for the BPF JIT codegen and drop __nocfi for x86. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20231215092707.345270396@infradead.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2023-12-15cfi: Flip headersPeter Zijlstra
Normal include order is that linux/foo.h should include asm/foo.h, CFI has it the wrong way around. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Sami Tolvanen <samitolvanen@google.com> Link: https://lore.kernel.org/r/20231215092707.231038174@infradead.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2022-09-26x86: Add support for CONFIG_CFI_CLANGSami Tolvanen
With CONFIG_CFI_CLANG, the compiler injects a type preamble immediately before each function and a check to validate the target function type before indirect calls: ; type preamble __cfi_function: mov <id>, %eax function: ... ; indirect call check mov -<id>,%r10d add -0x4(%r11),%r10d je .Ltmp1 ud2 .Ltmp1: call __x86_indirect_thunk_r11 Add error handling code for the ud2 traps emitted for the checks, and allow CONFIG_CFI_CLANG to be selected on x86_64. This produces the following oops on CFI failure (generated using lkdtm): [ 21.441706] CFI failure at lkdtm_indirect_call+0x16/0x20 [lkdtm] (target: lkdtm_increment_int+0x0/0x10 [lkdtm]; expected type: 0x7e0c52a) [ 21.444579] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI [ 21.445296] CPU: 0 PID: 132 Comm: sh Not tainted 5.19.0-rc8-00020-g9f27360e674c #1 [ 21.445296] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 21.445296] RIP: 0010:lkdtm_indirect_call+0x16/0x20 [lkdtm] [ 21.445296] Code: 52 1c c0 48 c7 c1 c5 50 1c c0 e9 25 48 2a cc 0f 1f 44 00 00 49 89 fb 48 c7 c7 50 b4 1c c0 41 ba 5b ad f3 81 45 03 53 f8 [ 21.445296] RSP: 0018:ffffa9f9c02ffdc0 EFLAGS: 00000292 [ 21.445296] RAX: 0000000000000027 RBX: ffffffffc01cb300 RCX: 385cbbd2e070a700 [ 21.445296] RDX: 0000000000000000 RSI: c0000000ffffdfff RDI: ffffffffc01cb450 [ 21.445296] RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8d081610 [ 21.445296] R10: 00000000bcc90825 R11: ffffffffc01c2fc0 R12: 0000000000000000 [ 21.445296] R13: ffffa31b827a6000 R14: 0000000000000000 R15: 0000000000000002 [ 21.445296] FS: 00007f08b42216a0(0000) GS:ffffa31b9f400000(0000) knlGS:0000000000000000 [ 21.445296] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 21.445296] CR2: 0000000000c76678 CR3: 0000000001940000 CR4: 00000000000006f0 [ 21.445296] Call Trace: [ 21.445296] <TASK> [ 21.445296] lkdtm_CFI_FORWARD_PROTO+0x30/0x50 [lkdtm] [ 21.445296] direct_entry+0x12d/0x140 [lkdtm] [ 21.445296] full_proxy_write+0x5d/0xb0 [ 21.445296] vfs_write+0x144/0x460 [ 21.445296] ? __x64_sys_wait4+0x5a/0xc0 [ 21.445296] ksys_write+0x69/0xd0 [ 21.445296] do_syscall_64+0x51/0xa0 [ 21.445296] entry_SYSCALL_64_after_hwframe+0x63/0xcd [ 21.445296] RIP: 0033:0x7f08b41a6fe1 [ 21.445296] Code: be 07 00 00 00 41 89 c0 e8 7e ff ff ff 44 89 c7 89 04 24 e8 91 c6 02 00 8b 04 24 48 83 c4 68 c3 48 63 ff b8 01 00 00 03 [ 21.445296] RSP: 002b:00007ffcdf65c2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 21.445296] RAX: ffffffffffffffda RBX: 00007f08b4221690 RCX: 00007f08b41a6fe1 [ 21.445296] RDX: 0000000000000012 RSI: 0000000000c738f0 RDI: 0000000000000001 [ 21.445296] RBP: 0000000000000001 R08: fefefefefefefeff R09: fefefefeffc5ff4e [ 21.445296] R10: 00007f08b42222b0 R11: 0000000000000246 R12: 0000000000c738f0 [ 21.445296] R13: 0000000000000012 R14: 00007ffcdf65c401 R15: 0000000000c70450 [ 21.445296] </TASK> [ 21.445296] Modules linked in: lkdtm [ 21.445296] Dumping ftrace buffer: [ 21.445296] (ftrace buffer empty) [ 21.471442] ---[ end trace 0000000000000000 ]--- [ 21.471811] RIP: 0010:lkdtm_indirect_call+0x16/0x20 [lkdtm] [ 21.472467] Code: 52 1c c0 48 c7 c1 c5 50 1c c0 e9 25 48 2a cc 0f 1f 44 00 00 49 89 fb 48 c7 c7 50 b4 1c c0 41 ba 5b ad f3 81 45 03 53 f8 [ 21.474400] RSP: 0018:ffffa9f9c02ffdc0 EFLAGS: 00000292 [ 21.474735] RAX: 0000000000000027 RBX: ffffffffc01cb300 RCX: 385cbbd2e070a700 [ 21.475664] RDX: 0000000000000000 RSI: c0000000ffffdfff RDI: ffffffffc01cb450 [ 21.476471] RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8d081610 [ 21.477127] R10: 00000000bcc90825 R11: ffffffffc01c2fc0 R12: 0000000000000000 [ 21.477959] R13: ffffa31b827a6000 R14: 0000000000000000 R15: 0000000000000002 [ 21.478657] FS: 00007f08b42216a0(0000) GS:ffffa31b9f400000(0000) knlGS:0000000000000000 [ 21.479577] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 21.480307] CR2: 0000000000c76678 CR3: 0000000001940000 CR4: 00000000000006f0 [ 21.481460] Kernel panic - not syncing: Fatal exception Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Tested-by: Kees Cook <keescook@chromium.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220908215504.3686827-23-samitolvanen@google.com
generated by cgit (git 2.34.1) at 2025-08-04 05:50:30 +0000