* Coverity: emulator_leave_smm(): Error handling issues
@ 2022-12-01 16:25 coverity-bot
2022-12-01 18:18 ` Sean Christopherson
0 siblings, 1 reply; 3+ messages in thread
From: coverity-bot @ 2022-12-01 16:25 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Sean Christopherson, x86, Maxim Levitsky, linux-kernel,
Borislav Petkov, Ingo Molnar, H. Peter Anvin, Thomas Gleixner,
kvm, Dave Hansen, Gustavo A. R. Silva, linux-next,
linux-hardening
Hello!
This is an experimental semi-automated report about issues detected by
Coverity from a scan of next-20221201 as part of the linux-next scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan
You're getting this email because you were associated with the identified
lines of code (noted below) that were touched by commits:
Wed Nov 9 12:31:18 2022 -0500
1d0da94cdafe ("KVM: x86: do not go through ctxt->ops when emulating rsm")
Coverity reported the following:
*** CID 1527763: Error handling issues (CHECKED_RETURN)
arch/x86/kvm/smm.c:631 in emulator_leave_smm()
625 cr4 = kvm_read_cr4(vcpu);
626 if (cr4 & X86_CR4_PAE)
627 kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PAE);
628
629 /* And finally go back to 32-bit mode. */
630 efer = 0;
vvv CID 1527763: Error handling issues (CHECKED_RETURN)
vvv Calling "kvm_set_msr" without checking return value (as is done elsewhere 5 out of 6 times).
631 kvm_set_msr(vcpu, MSR_EFER, efer);
632 }
633 #endif
634
635 /*
636 * Give leave_smm() a chance to make ISA-specific changes to the vCPU
If this is a false positive, please let us know so we can mark it as
such, or teach the Coverity rules to be smarter. If not, please make
sure fixes get into linux-next. :) For patches fixing this, please
include these lines (but double-check the "Fixes" first):
Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1527763 ("Error handling issues")
Fixes: 1d0da94cdafe ("KVM: x86: do not go through ctxt->ops when emulating rsm")
Thanks for your attention!
--
Coverity-bot
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Coverity: emulator_leave_smm(): Error handling issues
2022-12-01 16:25 Coverity: emulator_leave_smm(): Error handling issues coverity-bot
@ 2022-12-01 18:18 ` Sean Christopherson
2022-12-01 23:22 ` Kees Cook
0 siblings, 1 reply; 3+ messages in thread
From: Sean Christopherson @ 2022-12-01 18:18 UTC (permalink / raw)
To: coverity-bot
Cc: Paolo Bonzini, x86, Maxim Levitsky, linux-kernel,
Borislav Petkov, Ingo Molnar, H. Peter Anvin, Thomas Gleixner,
kvm, Dave Hansen, Gustavo A. R. Silva, linux-next,
linux-hardening
On Thu, Dec 01, 2022, coverity-bot wrote:
> Hello!
>
> This is an experimental semi-automated report about issues detected by
> Coverity from a scan of next-20221201 as part of the linux-next scan project:
> https://scan.coverity.com/projects/linux-next-weekly-scan
>
> You're getting this email because you were associated with the identified
> lines of code (noted below) that were touched by commits:
>
> Wed Nov 9 12:31:18 2022 -0500
> 1d0da94cdafe ("KVM: x86: do not go through ctxt->ops when emulating rsm")
>
> Coverity reported the following:
>
> *** CID 1527763: Error handling issues (CHECKED_RETURN)
> arch/x86/kvm/smm.c:631 in emulator_leave_smm()
> 625 cr4 = kvm_read_cr4(vcpu);
> 626 if (cr4 & X86_CR4_PAE)
> 627 kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PAE);
> 628
> 629 /* And finally go back to 32-bit mode. */
> 630 efer = 0;
> vvv CID 1527763: Error handling issues (CHECKED_RETURN)
> vvv Calling "kvm_set_msr" without checking return value (as is done elsewhere 5 out of 6 times).
> 631 kvm_set_msr(vcpu, MSR_EFER, efer);
> 632 }
> 633 #endif
> 634
> 635 /*
> 636 * Give leave_smm() a chance to make ISA-specific changes to the vCPU
>
> If this is a false positive, please let us know so we can mark it as
It's not a false positive per se, but absent a KVM bug the call can never fail.
Ditto for the kvm_set_cr{0,4}() calls above. That said, I'm tempted to "fix"
these since we've had bugs related to this code in the past. This doesn't seem
too ugly...
diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index a9c1c2af8d94..621e39689bff 100644
--- a/arch/x86/kvm/smm.c
+++ b/arch/x86/kvm/smm.c
@@ -601,8 +601,9 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
/* Zero CR4.PCIDE before CR0.PG. */
cr4 = kvm_read_cr4(vcpu);
- if (cr4 & X86_CR4_PCIDE)
- kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PCIDE);
+ if (cr4 & X86_CR4_PCIDE &&
+ WARN_ON_ONCE(kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PCIDE)))
+ return X86EMUL_UNHANDLEABLE;
/* A 32-bit code segment is required to clear EFER.LMA. */
memset(&cs_desc, 0, sizeof(cs_desc));
@@ -614,8 +615,9 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
/* For the 64-bit case, this will clear EFER.LMA. */
cr0 = kvm_read_cr0(vcpu);
- if (cr0 & X86_CR0_PE)
- kvm_set_cr0(vcpu, cr0 & ~(X86_CR0_PG | X86_CR0_PE));
+ if (cr0 & X86_CR0_PE &&
+ WARN_ON_ONCE(kvm_set_cr0(vcpu, cr0 & ~(X86_CR0_PG | X86_CR0_PE))))
+ return X86EMUL_UNHANDLEABLE;
#ifdef CONFIG_X86_64
if (guest_cpuid_has(vcpu, X86_FEATURE_LM)) {
@@ -623,12 +625,14 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
/* Clear CR4.PAE before clearing EFER.LME. */
cr4 = kvm_read_cr4(vcpu);
- if (cr4 & X86_CR4_PAE)
- kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PAE);
+ if ((cr4 & X86_CR4_PAE &&
+ WARN_ON_ONCE(kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PAE)))
+ return X86EMUL_UNHANDLEABLE;
/* And finally go back to 32-bit mode. */
efer = 0;
- kvm_set_msr(vcpu, MSR_EFER, efer);
+ if (WARN_ON_ONCE(kvm_set_msr(vcpu, MSR_EFER, efer)))
+ return X86EMUL_UNHANDLEABLE;
}
#endif
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: Coverity: emulator_leave_smm(): Error handling issues
2022-12-01 18:18 ` Sean Christopherson
@ 2022-12-01 23:22 ` Kees Cook
0 siblings, 0 replies; 3+ messages in thread
From: Kees Cook @ 2022-12-01 23:22 UTC (permalink / raw)
To: Sean Christopherson
Cc: Paolo Bonzini, x86, Maxim Levitsky, linux-kernel,
Borislav Petkov, Ingo Molnar, H. Peter Anvin, Thomas Gleixner,
kvm, Dave Hansen, Gustavo A. R. Silva, linux-next,
linux-hardening
On Thu, Dec 01, 2022 at 06:18:45PM +0000, Sean Christopherson wrote:
> On Thu, Dec 01, 2022, coverity-bot wrote:
> > Hello!
> >
> > This is an experimental semi-automated report about issues detected by
> > Coverity from a scan of next-20221201 as part of the linux-next scan project:
> > https://scan.coverity.com/projects/linux-next-weekly-scan
> >
> > You're getting this email because you were associated with the identified
> > lines of code (noted below) that were touched by commits:
> >
> > Wed Nov 9 12:31:18 2022 -0500
> > 1d0da94cdafe ("KVM: x86: do not go through ctxt->ops when emulating rsm")
> >
> > Coverity reported the following:
> >
> > *** CID 1527763: Error handling issues (CHECKED_RETURN)
> > arch/x86/kvm/smm.c:631 in emulator_leave_smm()
> > 625 cr4 = kvm_read_cr4(vcpu);
> > 626 if (cr4 & X86_CR4_PAE)
> > 627 kvm_set_cr4(vcpu, cr4 & ~X86_CR4_PAE);
> > 628
> > 629 /* And finally go back to 32-bit mode. */
> > 630 efer = 0;
> > vvv CID 1527763: Error handling issues (CHECKED_RETURN)
> > vvv Calling "kvm_set_msr" without checking return value (as is done elsewhere 5 out of 6 times).
> > 631 kvm_set_msr(vcpu, MSR_EFER, efer);
> > 632 }
> > 633 #endif
> > 634
> > 635 /*
> > 636 * Give leave_smm() a chance to make ISA-specific changes to the vCPU
> >
> > If this is a false positive, please let us know so we can mark it as
>
> It's not a false positive per se, but absent a KVM bug the call can never fail.
> Ditto for the kvm_set_cr{0,4}() calls above. That said, I'm tempted to "fix"
> these since we've had bugs related to this code in the past. This doesn't seem
> too ugly...
Yeah, that's what I've done with similar cases. "This should be
impossible" get a WARN_ONCE and fail gracefully.
-Kees
--
Kees Cook
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-12-01 16:25 Coverity: emulator_leave_smm(): Error handling issues coverity-bot
2022-12-01 18:18 ` Sean Christopherson
2022-12-01 23:22 ` Kees Cook
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