From 2c6636c82f8c6c18e18c085fe69d0cd3dbe3b991 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Pawe=C5=82=20Anikiel?= Date: Thu, 10 Apr 2025 11:54:20 +0000 Subject: [PATCH] x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST or Rust >= 1.88 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Calling core::fmt::write() from rust code while FineIBT is enabled results in a kernel panic: [ 4614.199779] kernel BUG at arch/x86/kernel/cet.c:132! [ 4614.205343] Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI [ 4614.211781] CPU: 2 UID: 0 PID: 6057 Comm: dmabuf_dump Tainted: G U O 6.12.17-android16-0-g6ab38c534a43 #1 9da040f27673ec3945e23b998a0f8bd64c846599 [ 4614.227832] Tainted: [U]=USER, [O]=OOT_MODULE [ 4614.241247] RIP: 0010:do_kernel_cp_fault+0xea/0xf0 [ 4614.246621] Code: c6 15 8d ad ac 48 0f 44 f1 48 8d 04 80 48 8d 14 45 d0 37 42 ac 48 c7 c7 22 99 bb ac e8 9f 7a 05 00 0f 0b eb 9a 67 0f b9 40 12 <0f> 0b cc cc cc cc 66 0f 1f 00 41 81 ea 00 00 00 00 74 03 0f 0b 90 [ 4614.267606] RSP: 0018:ffffb95acfa4b978 EFLAGS: 00010097 [ 4614.273464] RAX: 0000000000000057 RBX: ffffb95acfa4b9b8 RCX: 3ff1c813cb576300 [ 4614.281426] RDX: ffff9a50b792b8d0 RSI: ffff9a50b791d548 RDI: ffff9a50b791d548 [ 4614.289408] RBP: ffffb95acfa4b980 R08: 0000000000000d7c R09: ffffffffad45d500 [ 4614.297399] R10: 0000000000002874 R11: 0000000000000004 R12: 0000000000000000 [ 4614.305369] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000003 [ 4614.313345] FS: 000076fa106dcfe8(0000) GS:ffff9a50b7900000(0000) knlGS:0000000000000000 [ 4614.322386] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 4614.328806] CR2: 000076f8fc207bd0 CR3: 0000000227242000 CR4: 0000000000f52eb0 [ 4614.336777] PKRU: 55555554 [ 4614.339786] Call Trace: [ 4614.342524] [ 4614.344867] ? __die_body+0x69/0xb0 [ 4614.348786] ? die+0xa9/0xd0 [ 4614.352000] ? do_trap+0x89/0x160 [ 4614.355721] ? do_kernel_cp_fault+0xea/0xf0 [ 4614.360413] ? handle_invalid_op+0x69/0x90 [ 4614.364985] ? do_kernel_cp_fault+0xea/0xf0 [ 4614.369654] ? exc_invalid_op+0x36/0x60 [ 4614.373959] ? asm_exc_invalid_op+0x1f/0x30 [ 4614.378643] ? do_kernel_cp_fault+0xea/0xf0 [ 4614.383335] ? do_kernel_cp_fault+0x31/0xf0 [ 4614.388005] exc_control_protection+0x49/0x70 [ 4614.392871] asm_exc_control_protection+0x2b/0x60 [ 4614.398144] RIP: 0010:_RNvXs5_NtNtNtCs3o2tGsuHyou_4core3fmt3num3impyNtB9_7Display3fmt+0x0/0x20 [ 4614.407792] Code: 48 f7 df 48 0f 48 f9 48 89 f2 89 c6 5d e9 18 fd ff ff 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 41 81 ea 14 61 af 2c 74 03 0f 0b 90 <66> 0f 1f 00 55 48 89 e5 48 89 f2 48 8b 3f be 01 00 00 00 5d e9 e7 [ 4614.428775] RSP: 0018:ffffb95acfa4ba68 EFLAGS: 00010246 [ 4614.434609] RAX: 0000000000000000 RBX: 0000000000000010 RCX: 0000000000000000 [ 4614.442587] RDX: 0000000000000007 RSI: ffffb95acfa4ba70 RDI: ffffb95acfa4bc88 [ 4614.450557] RBP: ffffb95acfa4bae0 R08: ffff0a00ffffff05 R09: 0000000000000070 [ 4614.458527] R10: 0000000000000000 R11: ffffffffab67eaf0 R12: ffffb95acfa4bcc8 [ 4614.466493] R13: ffffffffac5d50f0 R14: 0000000000000000 R15: 0000000000000000 [ 4614.474473] ? __cfi__RNvXs5_NtNtNtCs3o2tGsuHyou_4core3fmt3num3impyNtB9_7Display3fmt+0x10/0x10 [ 4614.484118] ? _RNvNtCs3o2tGsuHyou_4core3fmt5write+0x1d2/0x250 This happens because core::fmt::write() calls core::fmt::rt::Argument::fmt(), which currently has CFI disabled: library/core/src/fmt/rt.rs: 171 // FIXME: Transmuting formatter in new and indirectly branching to/calling 172 // it here is an explicit CFI violation. 173 #[allow(inline_no_sanitize)] 174 #[no_sanitize(cfi, kcfi)] 175 #[inline] 176 pub(super) unsafe fn fmt(&self, f: &mut Formatter<'_>) -> Result { This causes a Control Protection exception, because FineIBT has sealed off the original function's endbr64. This makes rust currently incompatible with FineIBT. Add a Kconfig dependency that prevents FineIBT from getting turned on by default if rust is enabled. [ Rust 1.88.0 (scheduled for 2025-06-26) should have this fixed [1], and thus we relaxed the condition with Rust >= 1.88. When `objtool` lands checking for this with e.g. [2], the plan is to ideally run that in upstream Rust's CI to prevent regressions early [3], since we do not control `core`'s source code. Alice tested the Rust PR backported to an older compiler. - Miguel ] Signed-off-by: Paweł Anikiel Reviewed-by: Alice Ryhl Acked-by: Peter Zijlstra Link: https://github.com/rust-lang/rust/pull/139632 [1] Link: https://lore.kernel.org/rust-for-linux/20250410154556.GB9003@noisy.programming.kicks-ass.net/ [2] Link: https://github.com/rust-lang/rust/pull/139632#issuecomment-2801950873 [3] Link: https://lore.kernel.org/r/20250410115420.366349-1-panikiel@google.com Signed-off-by: Miguel Ojeda --- arch/x86/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 4b9f378e05f6..5873c9e39919 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2368,6 +2368,7 @@ config STRICT_SIGALTSTACK_SIZE config CFI_AUTO_DEFAULT bool "Attempt to use FineIBT by default at boot time" depends on FINEIBT + depends on !RUST || RUSTC_VERSION >= 108800 default y help Attempt to use FineIBT by default at boot time. If enabled, base-commit: c1b4071ec3a6a594df6c49bf8f04a60a88072525 -- 2.49.0