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Peter Anvin" , Andi Kleen , Tony Luck , linux-kernel@vger.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)), kvm@vger.kernel.org (open list:X86 TRUST DOMAIN EXTENSIONS (TDX)) Subject: [PATCH] x86/tdx: Fix zero-extension for CPUID emulation Date: Tue, 12 May 2026 23:37:19 +0200 Message-ID: <20260512213719.20974-1-clopez@suse.de> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Level: X-Rspamd-Action: no action X-Spamd-Result: default: False [-3.51 / 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]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[14]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; 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]; URIBL_BLOCKED(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim,suse.de:email,suse.de:mid]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Queue-Id: 7BCF66AAF8 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Score: -3.51 In the x86 architecture, 32-bit operations zero-extend the result in the destination register to 64 bits. This includes the CPUID instruction, which writes 32-bit values EAX/EBX/ECX/EDX. When handling the CPUID instruction via #VE, copy only the lower 32-bits provided by the hypervisor for the output registers, and zero out the upper half. Fixes: c141fa2c2bba ("x86/tdx: Handle CPUID via #VE") Cc: stable@vger.kernel.org Signed-off-by: Carlos López --- arch/x86/coco/tdx/tdx.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index c8b9e86d0488..a2fe1ae019bd 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -543,10 +543,10 @@ static int handle_cpuid(struct pt_regs *regs, struct ve_info *ve) * EAX, EBX, ECX, EDX registers after the CPUID instruction execution. * So copy the register contents back to pt_regs. */ - regs->ax = args.r12; - regs->bx = args.r13; - regs->cx = args.r14; - regs->dx = args.r15; + regs->ax = lower_32_bits(args.r12); + regs->bx = lower_32_bits(args.r13); + regs->cx = lower_32_bits(args.r14); + regs->dx = lower_32_bits(args.r15); return ve_instr_len(ve); } -- 2.51.0