From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
[ Upstream commit 3d9606b0e0f3aed4dfb61d0853ebf432fead7bba ]
The following BUG was reported:
traps: Missing ENDBR: andw_ax_dx+0x0/0x10 [kvm]
------------[ cut here ]------------
kernel BUG at arch/x86/kernel/traps.c:253!
invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
<TASK>
asm_exc_control_protection+0x2b/0x30
RIP: 0010:andw_ax_dx+0x0/0x10 [kvm]
Code: c3 cc cc cc cc 0f 1f 44 00 00 66 0f 1f 00 48 19 d0 c3 cc cc cc
cc 0f 1f 40 00 f3 0f 1e fa 20 d0 c3 cc cc cc cc 0f 1f 44 00 00
<66> 0f 1f 00 66 21 d0 c3 cc cc cc cc 0f 1f 40 00 66 0f 1f 00 21
d0
? andb_al_dl+0x10/0x10 [kvm]
? fastop+0x5d/0xa0 [kvm]
x86_emulate_insn+0x822/0x1060 [kvm]
x86_emulate_instruction+0x46f/0x750 [kvm]
complete_emulated_mmio+0x216/0x2c0 [kvm]
kvm_arch_vcpu_ioctl_run+0x604/0x650 [kvm]
kvm_vcpu_ioctl+0x2f4/0x6b0 [kvm]
? wake_up_q+0xa0/0xa0
The BUG occurred because the ENDBR in the andw_ax_dx() fastop function
had been incorrectly "sealed" (converted to a NOP) by apply_ibt_endbr().
Objtool marked it to be sealed because KVM has no compile-time
references to the function. Instead KVM calculates its address at
runtime.
Prevent objtool from annotating fastop functions as sealable by creating
throwaway dummy compile-time references to the functions.
Fixes: 6649fa876da4 ("x86/ibt,kvm: Add ENDBR to fastops")
Reported-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Debugged-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Message-Id: <0d4116f90e9d0c1b754bb90c585e6f0415a1c508.1660837839.git.jpoimboe@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/kvm/emulate.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index aa907cec0918..09fa8a94807b 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -316,7 +316,8 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
".align " __stringify(FASTOP_SIZE) " \n\t" \
".type " name ", @function \n\t" \
name ":\n\t" \
- ASM_ENDBR
+ ASM_ENDBR \
+ IBT_NOSEAL(name)
#define FOP_FUNC(name) \
__FOP_FUNC(#name)
--
2.35.1
