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b=owGbwMvMwCFmkMcZplerG8N4Wi2JIe1XAPP+CW6ZqxccPKowL43/Tf6HExp8dsf8IuIdo91Dp 38VbpvbUcrCIMbBICumyCIw+++7nacnStU6z5KFmcPKBDKEgYtTACZyP5ThD39HQciqZ45X7a+I V/w7Vrn2CUPYFo2E0GfiEzqK3SeJaDH8FaicbvpzA/e5xw8uM6jYfnfbb220fSNTS1jDbtfUmGu XuAE= X-Mailer: git-send-email 2.46.1.824.gd892dcdcdd-goog Message-ID: <20240930071513.909462-8-ardb+git@google.com> Subject: [PATCH v2 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: 1727680548534116600 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 | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index 64fca49cd88f..ce4fd8d33da4 100644 --- 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. --=20 2.46.1.824.gd892dcdcdd-goog From nobody Sun Nov 24 17:06:29 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; 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b=owGbwMvMwCFmkMcZplerG8N4Wi2JIe1XAMvKaXsePbde5td+dfnhwmiXT5KtMpOUj2dUMoenF PtWLmnoKGVhEONgkBVTZBGY/ffdztMTpWqdZ8nCzGFlAhnCwMUpABMxjWX4n/+KZ1mOY5Nuo17G w1N8j1fMPBPO8OCstkrBmZ0/Sus5axkZZtSdcld0/rF9HlvL4njeqq+1F5aYmnDrf7A/OrWtvjW CHQA= X-Mailer: git-send-email 2.46.1.824.gd892dcdcdd-goog Message-ID: <20240930071513.909462-9-ardb+git@google.com> Subject: [PATCH v2 2/5] x86/pvh: Use correct size value in GDT descriptor 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: 1727680550325116600 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel The limit field in a GDT descriptor is an inclusive bound, and therefore one less than the size of the covered range. Reviewed-by: Jason Andryuk Tested-by: Jason Andryuk Signed-off-by: Ard Biesheuvel --- arch/x86/platform/pvh/head.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index ce4fd8d33da4..5a196fb3ebd8 100644 --- a/arch/x86/platform/pvh/head.S +++ b/arch/x86/platform/pvh/head.S @@ -224,7 +224,7 @@ SYM_CODE_END(pvh_start_xen) .section ".init.data","aw" .balign 8 SYM_DATA_START_LOCAL(gdt) - .word gdt_end - gdt_start + .word gdt_end - gdt_start - 1 .long _pa(gdt_start) /* x86-64 will overwrite if relocated. */ .word 0 SYM_DATA_END(gdt) --=20 2.46.1.824.gd892dcdcdd-goog From nobody Sun Nov 24 17:06:29 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; 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charset="utf-8" From: Ard Biesheuvel Since commit d9ec1158056b ("x86/boot/64: Use RIP_REL_REF() to assign 'phys_base'") phys_base is assigned directly rather than added to, so it is no longer necessary to clear it after use. Reviewed-by: Jason Andryuk Tested-by: Jason Andryuk Signed-off-by: Ard Biesheuvel --- arch/x86/platform/pvh/head.S | 7 ------- 1 file changed, 7 deletions(-) diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index 5a196fb3ebd8..7ca51a4da217 100644 --- a/arch/x86/platform/pvh/head.S +++ b/arch/x86/platform/pvh/head.S @@ -180,13 +180,6 @@ SYM_CODE_START_LOCAL(pvh_start_xen) ANNOTATE_RETPOLINE_SAFE call *%rax =20 - /* - * Clear phys_base. __startup_64 will *add* to its value, - * so reset to 0. - */ - xor %rbx, %rbx - movq %rbx, phys_base(%rip) - /* startup_64 expects boot_params in %rsi. */ lea pvh_bootparams(%rip), %rsi jmp startup_64 --=20 2.46.1.824.gd892dcdcdd-goog From nobody Sun Nov 24 17:06:29 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; 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b=owGbwMvMwCFmkMcZplerG8N4Wi2JIe1XAPuhF2t5+zhSPgu3tTyOidS9aCBp1+yrcNT4n/r00 JmnTes7SlkYxDgYZMUUWQRm/3238/REqVrnWbIwc1iZQIYwcHEKwEQubGVkmJV+Ys/d2PLAmsCY qVKPXi7e52T1MUgu5MSrXwo3Q45OSWFk+F3/bv+942nVjqavFqjqp8r0qphbWB66/EGiOXxZ6qO DLAA= X-Mailer: git-send-email 2.46.1.824.gd892dcdcdd-goog Message-ID: <20240930071513.909462-11-ardb+git@google.com> Subject: [PATCH v2 4/5] x86/xen: Avoid relocatable quantities in Xen ELF notes 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: 1727680558381116600 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel Xen puts virtual and physical addresses into ELF notes that are treated by the linker as relocatable by default. Doing so is not only pointless, given that the ELF notes are only intended for consumption by Xen before the kernel boots. It is also a KASLR leak, given that the kernel's ELF notes are exposed via the world readable /sys/kernel/notes. So emit these constants in a way that prevents the linker from marking them as relocatable. This involves place-relative relocations (which subtract their own virtual address from the symbol value) and linker provided absolute symbols that add the address of the place to the desired value. Signed-off-by: Ard Biesheuvel Tested-by: Jason Andryuk --- arch/x86/kernel/vmlinux.lds.S | 13 +++++++++++++ arch/x86/platform/pvh/head.S | 6 +++--- arch/x86/tools/relocs.c | 1 + arch/x86/xen/xen-head.S | 6 ++++-- 4 files changed, 21 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 6726be89b7a6..2b7c8c14c6fd 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -527,3 +527,16 @@ INIT_PER_CPU(irq_stack_backing_store); #endif =20 #endif /* CONFIG_X86_64 */ + +#ifdef CONFIG_XEN +#ifdef CONFIG_XEN_PV +xen_elfnote_entry_offset =3D + ABSOLUTE(xen_elfnote_entry) + ABSOLUTE(startup_xen); +#endif +xen_elfnote_hypercall_page_offset =3D + ABSOLUTE(xen_elfnote_hypercall_page) + ABSOLUTE(hypercall_page); +#endif +#ifdef CONFIG_PVH +xen_elfnote_phys32_entry_offset =3D + ABSOLUTE(xen_elfnote_phys32_entry) + ABSOLUTE(pvh_start_xen - LOAD_OFFSET= ); +#endif diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index 7ca51a4da217..2b0d887e0872 100644 --- a/arch/x86/platform/pvh/head.S +++ b/arch/x86/platform/pvh/head.S @@ -52,7 +52,7 @@ #define PVH_CS_SEL (PVH_GDT_ENTRY_CS * 8) #define PVH_DS_SEL (PVH_GDT_ENTRY_DS * 8) =20 -SYM_CODE_START_LOCAL(pvh_start_xen) +SYM_CODE_START(pvh_start_xen) UNWIND_HINT_END_OF_STACK cld =20 @@ -300,5 +300,5 @@ SYM_DATA_END(pvh_level2_kernel_pgt) .long KERNEL_IMAGE_SIZE - 1) #endif =20 - ELFNOTE(Xen, XEN_ELFNOTE_PHYS32_ENTRY, - _ASM_PTR (pvh_start_xen - __START_KERNEL_map)) + ELFNOTE(Xen, XEN_ELFNOTE_PHYS32_ENTRY, .global xen_elfnote_phys32_entry; + xen_elfnote_phys32_entry: _ASM_PTR xen_elfnote_phys32_entry_offset - .) diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index c101bed61940..3ede19ca8432 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -56,6 +56,7 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = =3D { [S_ABS] =3D "^(xen_irq_disable_direct_reloc$|" "xen_save_fl_direct_reloc$|" + "xen_elfnote_.+_offset$|" "VDSO|" "__kcfi_typeid_|" "__crc_)", diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 758bcd47b72d..3deaae3601f7 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -94,7 +94,8 @@ SYM_CODE_END(xen_cpu_bringup_again) ELFNOTE(Xen, XEN_ELFNOTE_VIRT_BASE, _ASM_PTR __START_KERNEL_map) /* Map the p2m table to a 512GB-aligned user address. */ ELFNOTE(Xen, XEN_ELFNOTE_INIT_P2M, .quad (PUD_SIZE * PTRS_PER_PUD)) - ELFNOTE(Xen, XEN_ELFNOTE_ENTRY, _ASM_PTR startup_xen) + ELFNOTE(Xen, XEN_ELFNOTE_ENTRY, .globl xen_elfnote_entry; + xen_elfnote_entry: _ASM_PTR xen_elfnote_entry_offset - .) 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b=owGbwMvMwCFmkMcZplerG8N4Wi2JIe1XAEestNQGk6l50lmPs5eufzv/6Lmly76atGQ+v9Td+ ewGZyprRykLgxgHg6yYIovA7L/vdp6eKFXrPEsWZg4rE8gQBi5OAZiI/HmG/+4pHxsFSpvWz+3h OKl79PF2Vud3V+eaLVi24Y1424yTaUsYGXatXdDioZAscT/1TO/jQ6Gq9w1elZ7/7bfv2KxbgaU /y1gB X-Mailer: git-send-email 2.46.1.824.gd892dcdcdd-goog Message-ID: <20240930071513.909462-12-ardb+git@google.com> Subject: [PATCH v2 5/5] x86/pvh: Avoid absolute symbol references in .head.text 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: 1727680562523116600 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel The .head.text section contains code that may execute from a different address than it was linked at. This is fragile, given that the x86 ABI can refer to global symbols via absolute or relative references, and the toolchain assumes that these are interchangeable, which they are not in this particular case. For this reason, all absolute symbol references are being removed from code that is emitted into .head.text. Subsequently, build time validation may be added that ensures that no absolute ELF relocations exist at all in that ELF section. In the case of the PVH code, the absolute references are in 32-bit code, which gets emitted with R_X86_64_32 relocations, and these are even more problematic going forward, as it prevents running the linker in PIE mode. So update the 64-bit code to avoid _pa(), and to only rely on relative symbol references: these are always 32-bits wide, even in 64-bit code, and are resolved by the linker at build time. Reviewed-by: Jason Andryuk Tested-by: Jason Andryuk Signed-off-by: Ard Biesheuvel --- arch/x86/platform/pvh/head.S | 30 ++++++++++++-------- 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S index 2b0d887e0872..cf89b2385c5a 100644 --- a/arch/x86/platform/pvh/head.S +++ b/arch/x86/platform/pvh/head.S @@ -6,7 +6,9 @@ =20 .code32 .text +#ifdef CONFIG_X86_32 #define _pa(x) ((x) - __START_KERNEL_map) +#endif #define rva(x) ((x) - pvh_start_xen) =20 #include @@ -72,8 +74,7 @@ SYM_CODE_START(pvh_start_xen) movl $0, %esp =20 leal rva(gdt)(%ebp), %eax - leal rva(gdt_start)(%ebp), %ecx - movl %ecx, 2(%eax) + addl %eax, 2(%eax) lgdt (%eax) =20 mov $PVH_DS_SEL,%eax @@ -103,10 +104,23 @@ SYM_CODE_START(pvh_start_xen) btsl $_EFER_LME, %eax wrmsr =20 + /* + * Reuse the non-relocatable symbol emitted for the ELF note to + * subtract the build time physical address of pvh_start_xen() from + * its actual runtime address, without relying on absolute 32-bit ELF + * relocations, as these are not supported by the linker when running + * in -pie mode, and should be avoided in .head.text in general. + */ mov %ebp, %ebx - subl $_pa(pvh_start_xen), %ebx /* offset */ + subl rva(xen_elfnote_phys32_entry)(%ebp), %ebx jz .Lpagetable_done =20 + /* + * Store the resulting load offset in phys_base. __pa() needs + * phys_base set to calculate the hypercall page in xen_pvh_init(). + */ + movl %ebx, rva(phys_base)(%ebp) + /* Fixup page-tables for relocation. */ leal rva(pvh_init_top_pgt)(%ebp), %edi movl $PTRS_PER_PGD, %ecx @@ -165,14 +179,6 @@ SYM_CODE_START(pvh_start_xen) xor %edx, %edx wrmsr =20 - /* - * Calculate load offset and store in phys_base. __pa() needs - * phys_base set to calculate the hypercall page in xen_pvh_init(). - */ - movq %rbp, %rbx - subq $_pa(pvh_start_xen), %rbx - movq %rbx, phys_base(%rip) - /* Call xen_prepare_pvh() via the kernel virtual mapping */ leaq xen_prepare_pvh(%rip), %rax subq phys_base(%rip), %rax @@ -218,7 +224,7 @@ SYM_CODE_END(pvh_start_xen) .balign 8 SYM_DATA_START_LOCAL(gdt) .word gdt_end - gdt_start - 1 - .long _pa(gdt_start) /* x86-64 will overwrite if relocated. */ + .long gdt_start - gdt .word 0 SYM_DATA_END(gdt) SYM_DATA_START_LOCAL(gdt_start) --=20 2.46.1.824.gd892dcdcdd-goog