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x86/xen: fix xen_hypercall_hvm() to not clobber %rbx

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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 using an already saved register instead of %rbx.

Fixes: b4845bb638 ("x86/xen: add central hypercall functions")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2025-02-05 09:43:31 +01:00
parent bda50f7770
commit 98a5cfd232
1 changed files with 2 additions and 2 deletions
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4
arch/x86/xen/xen-head.S
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@ -117,8 +117,8 @@ SYM_FUNC_START(xen_hypercall_hvm)
pop %ebx
pop %eax
#else
lea xen_hypercall_amd(%rip), %rbx
cmp %rax, %rbx
lea xen_hypercall_amd(%rip), %rcx
cmp %rax, %rcx
#ifdef CONFIG_FRAME_POINTER
pop %rax /* Dummy pop. */
#endif