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Peter Anvin" , xen-devel@lists.xenproject.org Subject: [PATCH] x86/xen: fix xen_hypercall_hvm() to not clobber %rbx Date: Wed, 5 Feb 2025 10:10:56 +0100 Message-ID: <20250205091056.17796-1-jgross@suse.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Spam-Level: X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[99.99%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[10]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[] X-Spam-Score: -2.80 X-Spam-Flag: NO Content-Type: text/plain; charset="utf-8" xen_hypercall_hvm(), which is used when running as a Xen PVH guest at most only once during early boot, is clobbering %rbx. Depending on whether the caller relies on %rbx to be preserved across the call or not, this clobbering might result in an early crash of the system. This can be avoided by not modifying %rbx in xen_hypercall_hvm(). Fixes: b4845bb63838 ("x86/xen: add central hypercall functions") Signed-off-by: Juergen Gross --- arch/x86/xen/xen-head.S | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 9252652afe59..4378b817ed32 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -117,8 +117,7 @@ SYM_FUNC_START(xen_hypercall_hvm) pop %ebx pop %eax #else - lea xen_hypercall_amd(%rip), %rbx - cmp %rax, %rbx + cmp xen_hypercall_amd(%rip), %rax #ifdef CONFIG_FRAME_POINTER pop %rax /* Dummy pop. */ #endif --=20 2.43.0