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KVM: VMX: Make VMREAD error path play nice with noinstr

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Mark vmread_error_trampoline() as noinstr, and add a second trampoline
for the CONFIG_CC_HAS_ASM_GOTO_OUTPUT=n case to enable instrumentation
when handling VM-Fail on VMREAD.  VMREAD is used in various noinstr
flows, e.g. immediately after VM-Exit, and objtool rightly complains that
the call to the error trampoline leaves a no-instrumentation section
without annotating that it's safe to do so.

  vmlinux.o: warning: objtool: vmx_vcpu_enter_exit+0xc9:
  call to vmread_error_trampoline() leaves .noinstr.text section

Note, strictly speaking, enabling instrumentation in the VM-Fail path
isn't exactly safe, but if VMREAD fails the kernel/system is likely hosed
anyways, and logging that there is a fatal error is more important than
*maybe* encountering slightly unsafe instrumentation.

Reported-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230721235637.2345403-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-07-21 16:56:36 -07:00 committed by Paolo Bonzini
parent 5e1fe4a21c
commit c20d403fd0
3 changed files with 27 additions and 10 deletions
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8
arch/x86/kvm/vmx/vmenter.S
View file

@ -303,10 +303,8 @@ SYM_FUNC_START(vmx_do_nmi_irqoff)
VMX_DO_EVENT_IRQOFF call asm_exc_nmi_kvm_vmx
SYM_FUNC_END(vmx_do_nmi_irqoff)
.section .text, "ax"
#ifndef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
/**
* vmread_error_trampoline - Trampoline from inline asm to vmread_error()
* @field: VMCS field encoding that failed
@ -335,7 +333,7 @@ SYM_FUNC_START(vmread_error_trampoline)
mov 3*WORD_SIZE(%_ASM_BP), %_ASM_ARG2
mov 2*WORD_SIZE(%_ASM_BP), %_ASM_ARG1
call vmread_error
call vmread_error_trampoline2
/* Zero out @fault, which will be popped into the result register. */
_ASM_MOV $0, 3*WORD_SIZE(%_ASM_BP)
@ -357,6 +355,8 @@ SYM_FUNC_START(vmread_error_trampoline)
SYM_FUNC_END(vmread_error_trampoline)
#endif
.section .text, "ax"
SYM_FUNC_START(vmx_do_interrupt_irqoff)
VMX_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
SYM_FUNC_END(vmx_do_interrupt_irqoff)

20
arch/x86/kvm/vmx/vmx.c
View file

@ -441,14 +441,24 @@ do { \
pr_warn_ratelimited(fmt); \
} while (0)
void vmread_error(unsigned long field, bool fault)
noinline void vmread_error(unsigned long field)
{
if (fault)
kvm_spurious_fault();
else
vmx_insn_failed("vmread failed: field=%lx\n", field);
vmx_insn_failed("vmread failed: field=%lx\n", field);
}
#ifndef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
noinstr void vmread_error_trampoline2(unsigned long field, bool fault)
{
if (fault) {
kvm_spurious_fault();
} else {
instrumentation_begin();
vmread_error(field);
instrumentation_end();
}
}
#endif
noinline void vmwrite_error(unsigned long field, unsigned long value)
{
vmx_insn_failed("vmwrite failed: field=%lx val=%lx err=%u\n",

9
arch/x86/kvm/vmx/vmx_ops.h
View file

@ -10,7 +10,7 @@
#include "vmcs.h"
#include "../x86.h"
void vmread_error(unsigned long field, bool fault);
void vmread_error(unsigned long field);
void vmwrite_error(unsigned long field, unsigned long value);
void vmclear_error(struct vmcs *vmcs, u64 phys_addr);
void vmptrld_error(struct vmcs *vmcs, u64 phys_addr);
@ -31,6 +31,13 @@ void invept_error(unsigned long ext, u64 eptp, gpa_t gpa);
* void vmread_error_trampoline(unsigned long field, bool fault);
*/
extern unsigned long vmread_error_trampoline;
/*
* The second VMREAD error trampoline, called from the assembly trampoline,
* exists primarily to enable instrumentation for the VM-Fail path.
*/
void vmread_error_trampoline2(unsigned long field, bool fault);
#endif
static __always_inline void vmcs_check16(unsigned long field)