This is a note to let you know that I've just added the patch titled
x86/pvh: Call C code via the kernel virtual mapping
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-pvh-call-c-code-via-the-kernel-virtual-mapping.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 981a05a2e3d15cf30f556fa08c217a6c8f0eda22
Author: Ard Biesheuvel <ardb@xxxxxxxxxx>
Date: Wed Oct 9 18:04:40 2024 +0200
x86/pvh: Call C code via the kernel virtual mapping
[ Upstream commit e8fbc0d9cab6c1ee6403f42c0991b0c1d5dbc092 ]
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@xxxxxxx>
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Message-ID: <20241009160438.3884381-8-ardb+git@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index cfabc3340362b..eadadd2ecd847 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -106,7 +106,14 @@ 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.
