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bh=W/PjtAFD7kN1k373OiTnMpXJo6wSfCFewIb7shmRoAo=; b=eWIvMjcR2w2Szi9tvlUj/PBm2DwWXFJEV6+2klCghZf1r9mpzHJQsSclQG/T7mwfY0uiQo rMtKbbqzVOerG0czLj1WllEinByD4lSHtLn93sBH0+1z7g/qOd18ASqqXmXgniWL7fCCaj U249HiTnjWRQTmgbdVAvXjFEVHgaw54= Date: Wed, 17 Feb 2021 19:00:09 +0100 From: Borislav Petkov To: Joerg Roedel Subject: Re: [PATCH 2/3] x86/sev-es: Check if regs->sp is trusted before adjusting #VC IST stack Message-ID: <20210217180009.GB6479@zn.tnic> References: <20210217120143.6106-1-joro@8bytes.org> <20210217120143.6106-3-joro@8bytes.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210217120143.6106-3-joro@8bytes.org> Cc: kvm@vger.kernel.org, Peter Zijlstra , Dave Hansen , virtualization@lists.linux-foundation.org, Arvind Sankar , hpa@zytor.com, Jiri Slaby , x86@kernel.org, David Rientjes , Martin Radev , Tom Lendacky , Joerg Roedel , Kees Cook , Cfir Cohen , Andy Lutomirski , Dan Williams , Juergen Gross , Mike Stunes , Sean Christopherson , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Masami Hiramatsu , Erdem Aktas X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Wed, Feb 17, 2021 at 01:01:42PM +0100, Joerg Roedel wrote: > From: Joerg Roedel > > The code in the NMI handler to adjust the #VC handler IST stack is > needed in case an NMI hits when the #VC handler is still using its IST > stack. > But the check for this condition also needs to look if the regs->sp > value is trusted, meaning it was not set by user-space. Extend the > check to not use regs->sp when the NMI interrupted user-space code or > the SYSCALL gap. > > Reported-by: Andy Lutomirski > Fixes: 315562c9af3d5 ("x86/sev-es: Adjust #VC IST Stack on entering NMI handler") > Cc: stable@vger.kernel.org # 5.10+ > Signed-off-by: Joerg Roedel > --- > arch/x86/kernel/sev-es.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c > index 84c1821819af..0df38b185d53 100644 > --- a/arch/x86/kernel/sev-es.c > +++ b/arch/x86/kernel/sev-es.c > @@ -144,7 +144,9 @@ void noinstr __sev_es_ist_enter(struct pt_regs *regs) > old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]); > > /* Make room on the IST stack */ > - if (on_vc_stack(regs->sp)) > + if (on_vc_stack(regs->sp) && > + !user_mode(regs) && > + !from_syscall_gap(regs)) Why not add those checks to on_vc_stack() directly? Because in it, you can say: on_vc_stack(): /* user mode rSP is not trusted */ if (user_mode()) return false; /* ditto */ if (ip_within_syscall_gap()) return false; ... ? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization