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Peter Anvin" , Jue Wang , linux-kernel@vger.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)) Subject: [PATCH] KVM: x86: Fix array_index_nospec() protection in kvm_vcpu_ioctl_x86_set_mce() Date: Sat, 16 May 2026 18:34:12 +0200 Message-ID: <20260516163412.601908-1-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-Level: X-Rspamd-Action: no action X-Spamd-Result: default: False [-3.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from,2a07:de40:b281:106:10:150:64:167:received]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim,suse.de:email,suse.de:mid]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Queue-Id: 410286BADE X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Score: -3.51 Commit aebc3ca19063 ("KVM: x86: Enable CMCI capability by default and handle injected UCNA errors") introduced kvm_vcpu_x86_set_ucna(), which accesses @vcpu->arch.mci_ctl2_banks[] using @mce->bank as the index. The @mce struct is user-controlled, provided via the KVM_X86_SET_MCE ioctl. The caller of this function, kvm_vcpu_ioctl_x86_set_mce(), bounds-checks @mce->bank and applies array_index_nospec() to advance the @banks pointer, but @mce->bank itself is passed through unclamped. On a speculative path that bypasses the bounds check, the raw @mce->bank value can index mci_ctl2_banks[] out-of-bounds. In practice this is a very weak gadget, and would at most allow leaking a single bit in a 64-bit integer, but prevent potential future issues by clamping @mce->bank in place with array_index_nospec(), before passing the struct to kvm_vcpu_x86_set_ucna(). Fixes: aebc3ca19063 ("KVM: x86: Enable CMCI capability by default and handl= e injected UCNA errors") Signed-off-by: Carlos L=C3=B3pez --- arch/x86/kvm/x86.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 209eae67ab18..2d2415031267 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5497,7 +5497,8 @@ static int kvm_vcpu_ioctl_x86_set_mce(struct kvm_vcpu= *vcpu, if (mce->bank >=3D bank_num || !(mce->status & MCI_STATUS_VAL)) return -EINVAL; =20 - banks +=3D array_index_nospec(4 * mce->bank, 4 * bank_num); + mce->bank =3D array_index_nospec(mce->bank, bank_num); + banks +=3D 4 * mce->bank; =20 if (is_ucna(mce)) return kvm_vcpu_x86_set_ucna(vcpu, mce, banks); base-commit: a9512a611bd030088f13477258d1f8103cceaa40 --=20 2.51.0