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bh=ikF+DtANi/r1AIRSe1GmX1n1cKKTQvrQZuBTXHOwalI=; b=VoakXUJf7UNGU/ZK9rrNZqSqDQ/w7mDwUvLKaySxuyE9FayNgeptz6FU6pbTfyPd2HnxXI tHZoEmTmFuLB2sBw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 07FF513254; Mon, 5 Aug 2024 20:20:43 +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 fYYNMBs0sWYcNAAAD6G6ig (envelope-from ); Mon, 05 Aug 2024 20:20:43 +0000 From: Fabiano Rosas To: qemu-devel@nongnu.org Cc: Paolo Bonzini , jpoimboe@kernel.org, Babu Moger , Dario Faggioli , Fabian Vogt , Nikolay Borisov Subject: [PATCH] target/i386: Expose IBPB-BRTYPE and SBPB CPUID bits to the guest Date: Mon, 5 Aug 2024 17:20:41 -0300 Message-Id: <20240805202041.5936-1-farosas@suse.de> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-5.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; DWL_DNSWL_MED(-2.00)[suse.de:dkim]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; R_MISSING_CHARSET(0.50)[]; 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_BLOCKED(0.00)[rspamd.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Action: no action X-Rspamd-Queue-Id: 1E39F21C89 Received-SPF: pass client-ip=195.135.223.130; envelope-from=farosas@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org According to AMD's Speculative Return Stack Overflow whitepaper (link below), the hypervisor should synthesize the value of IBPB_BRTYPE and SBPB CPUID bits to the guest. Support for this is already present in the kernel with commit e47d86083c66 ("KVM: x86: Add SBPB support") and commit 6f0f23ef76be ("KVM: x86: Add IBPB_BRTYPE support"). Add support in QEMU to expose the bits to the guest OS. host: # cat /sys/devices/system/cpu/vulnerabilities/spec_rstack_overflow Mitigation: Safe RET before (guest): $ cpuid -l 0x80000021 -1 -r 0x80000021 0x00: eax=0x00000045 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 ^ $ cat /sys/devices/system/cpu/vulnerabilities/spec_rstack_overflow Vulnerable: Safe RET, no microcode after (guest): $ cpuid -l 0x80000021 -1 -r 0x80000021 0x00: eax=0x18000045 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 ^ $ cat /sys/devices/system/cpu/vulnerabilities/spec_rstack_overflow Mitigation: Safe RET Reported-by: Fabian Vogt Link: https://www.amd.com/content/dam/amd/en/documents/corporate/cr/speculative-return-stack-overflow-whitepaper.pdf Signed-off-by: Fabiano Rosas --- More info on this thread: https://lore.kernel.org/r/68f8b8b1ca1bf58b059f52afbd1c9c51108a074a.camel@suse.com --- target/i386/cpu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 85ef7452c0..d33401c922 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -1221,8 +1221,8 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = { NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, - NULL, NULL, NULL, NULL, - NULL, NULL, NULL, NULL, + NULL, NULL, NULL, "sbpb", + "ibpb-brtype", NULL, NULL, NULL, }, .cpuid = { .eax = 0x80000021, .reg = R_EAX, }, .tcg_features = 0,