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

commit e8fbc0d9cab6c1ee6403f42c0991b0c1d5dbc092 upstream.

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>
[ Stable context update ]
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index 72c1e42d121df59d8454f84b6ddeb113f5740931..b3e3f64d436d8fbbc15783379304ec3edeb62b5f 100644 (file)
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -99,7 +99,12 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
        xor %edx, %edx
        wrmsr
 
-       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
 
        /* startup_64 expects boot_params in %rsi. */
        mov $_pa(pvh_bootparams), %rsi