[PATCH] x86/Kconfig: make CFI_AUTO_DEFAULT depend on !RUST
From: Paweł Anikiel
Date: Thu Apr 10 2025 - 08:02:53 EST
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] <TASK>
[ 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.
Signed-off-by: Paweł Anikiel <panikiel@xxxxxxxxxx>
---
arch/x86/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4b9f378e05f6..b31811a92286 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2367,7 +2367,7 @@ config STRICT_SIGALTSTACK_SIZE
config CFI_AUTO_DEFAULT
bool "Attempt to use FineIBT by default at boot time"
- depends on FINEIBT
+ depends on FINEIBT && !RUST
default y
help
Attempt to use FineIBT by default at boot time. If enabled,
--
2.49.0.504.g3bcea36a83-goog