x86/pvh: Call C code via the kernel virtual mapping

Calling C code via a different mapping than it was linked at is
problematic, because the compiler assumes that RIP-relative and absolute
symbol references are interchangeable. GCC in particular may use
RIP-relative per-CPU variable references even when not using -fpic.

So call xen_prepare_pvh() via its kernel virtual mapping on x86_64, so
that those RIP-relative references produce the correct values. This
matches the pre-existing behavior for i386, which also invokes
xen_prepare_pvh() via the kernel virtual mapping before invoking
startup_32 with paging disabled again.

Fixes: 7243b93345f7 ("xen/pvh: Bootstrap PVH guest")
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20241009160438.3884381-8-ardb+git@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index 64fca49cd88ff9bfd8cd697e5cd4ab94450a6033..ce4fd8d33da4672a18da13c3f11a32c0ff096fb0 100644 (file)
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -172,7 +172,14 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
        movq %rbp, %rbx
        subq $_pa(pvh_start_xen), %rbx
        movq %rbx, phys_base(%rip)
-       call xen_prepare_pvh
+
+       /* Call xen_prepare_pvh() via the kernel virtual mapping */
+       leaq xen_prepare_pvh(%rip), %rax
+       subq phys_base(%rip), %rax
+       addq $__START_KERNEL_map, %rax
+       ANNOTATE_RETPOLINE_SAFE
+       call *%rax
+
        /*
         * Clear phys_base.  __startup_64 will *add* to its value,
         * so reset to 0.