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

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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: 7243b93345 ("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>
This commit is contained in:
Ard Biesheuvel 2024-10-09 18:04:40 +02:00 committed by Juergen Gross
parent 8198375843
commit e8fbc0d9ca
1 changed files with 8 additions and 1 deletions
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9
arch/x86/platform/pvh/head.S
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@ -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.