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b=owGbwMvMwCFmkMcZplerG8N4Wi2JIe2rlfekYxbphgk37j1fI2+6+6JyzKRrSvf5uPkYr2770 /vy3/atHaUsDGIcDLJiiiwCs/++23l6olSt8yxZmDmsTCBDGLg4BWAiV4oY/uneq+0IOFzKn64x 6dHOnxXrpRKSfhs4zFp0WuTkvae5c6cxMhxm0Y98ri366awCh9g15YlN/ov+djz78lvU7gN3WcX 8FTwA X-Mailer: git-send-email 2.46.0.792.g87dc391469-goog Message-ID: <20240926104113.80146-8-ardb+git@google.com> Subject: [PATCH 1/5] x86/pvh: Call C code via the kernel virtual mapping From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: Ard Biesheuvel , Jason Andryuk , Juergen Gross , Boris Ostrovsky , x86@kernel.org, xen-devel@lists.xenproject.org X-ZohoMail-DKIM: pass (identity @google.com) X-ZM-MESSAGEID: 1727347330942116600 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel 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 Reviewed-by: Jason Andryuk Signed-off-by: Ard Biesheuvel --- arch/x86/platform/pvh/head.S | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index 64fca49cd88f..98ddd552885a 100644 --- a/arch/x86/platform/pvh/head.S +++ b/arch/x86/platform/pvh/head.S @@ -172,7 +172,13 @@ 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 + addq $__START_KERNEL_map, %rax + ANNOTATE_RETPOLINE_SAFE + call *%rax + /* * Clear phys_base. __startup_64 will *add* to its value, * so reset to 0. --=20 2.46.0.792.g87dc391469-goog