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Mon, 1 Jun 2026 13:34:25 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id zDeiFmGKHWreSAAAD6G6ig (envelope-from ); Mon, 01 Jun 2026 13:34:25 +0000 From: =?UTF-8?q?Carlos=20L=C3=B3pez?= To: kvm@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com Cc: =?UTF-8?q?Carlos=20L=C3=B3pez?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)), "H. Peter Anvin" , linux-kernel@vger.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)) Subject: [PATCH] KVM: x86: fix #GP check in em_dr_write() Date: Mon, 1 Jun 2026 15:33:21 +0200 Message-ID: <20260601133320.91479-2-clopez@suse.de> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Spam-Flag: NO X-Spam-Score: -3.30 X-Spamd-Result: default: False [-3.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:mid] X-Spam-Level: When emulating a MOV to a debug register, em_dr_write() calls @ctxt->ops->set_dr(), which is forwarded to emulator_set_dr() and then kvm_set_dr(). The latter checks that the written value is valid, otherwise returning an error, in which case the emulator is supposed to inject a #GP fault into the guest. Commit 996ff5429e98 ("KVM: x86: move kvm_inject_gp up from kvm_set_dr to callers") changed the contract of kvm_set_dr() (and thus emulator_set_dr()), returning 1 as an error instead of -1, but the caller in em_dr_write() was never updated, checking only if the returned value is negative. The end result is that em_dr_write() does not detect the error, so an invalid write does not generate a #GP, but at the same time the register value is not updated. The practical impact is limited, as check_dr_write() already checks DR6 and DR7 manually. However, it misses DR4/DR5, which alias DR6/DR7 when CR4.DE=3D0. Fix this by treating any non-zero return from set_dr() as a reason to inject #GP. Fixes: 996ff5429e98 ("KVM: x86: move kvm_inject_gp up from kvm_set_dr to ca= llers") Signed-off-by: Carlos L=C3=B3pez --- arch/x86/kvm/emulate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 585a8ceab220..de138ef92dc6 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -3299,7 +3299,7 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt) val =3D ctxt->src.val & ~0U; =20 /* #UD condition is already handled. */ - if (ctxt->ops->set_dr(ctxt, ctxt->modrm_reg, val) < 0) + if (ctxt->ops->set_dr(ctxt, ctxt->modrm_reg, val) !=3D 0) return emulate_gp(ctxt, 0); =20 /* Disable writeback. */ base-commit: d1568b1332b6b3b36b222c2868fc102727c12a34 --=20 2.51.0