Messages in this thread Patch in this message | | | From | Josh Poimboeuf <> | Subject | [PATCH 3/3] x86/kvm: Fix "missing ENDBR" BUG for fastop functions | Date | Thu, 18 Aug 2022 08:53:43 -0700 |
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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@intel.com> Debugged-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> --- 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 205d566ebd72..f092c54d1a2f 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -326,7 +326,8 @@ 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) -- 2.37.2
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