From: Ard Biesheuvel Date: Wed, 9 Oct 2024 16:04:43 +0000 (+0200) Subject: x86/xen: Avoid relocatable quantities in Xen ELF notes X-Git-Tag: v6.13-rc1~202^2~2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=223abe96ac0d227b22d48ab447dd9384b7a6c9fa;p=thirdparty%2Fkernel%2Flinux.git x86/xen: Avoid relocatable quantities in Xen ELF notes 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. Tested-by: Jason Andryuk Signed-off-by: Ard Biesheuvel Reviewed-by: Jason Andryuk Message-ID: <20241009160438.3884381-11-ardb+git@google.com> Signed-off-by: Juergen Gross --- diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index b8c5741d2fb48..60e5ac9b64e6e 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -528,3 +528,22 @@ INIT_PER_CPU(irq_stack_backing_store); #endif #endif /* CONFIG_X86_64 */ + +/* + * The symbols below are referenced using relative relocations in the + * respective ELF notes. This produces build time constants that the + * linker will never mark as relocatable. (Using just ABSOLUTE() is not + * sufficient for that). + */ +#ifdef CONFIG_XEN +#ifdef CONFIG_XEN_PV +xen_elfnote_entry_value = + ABSOLUTE(xen_elfnote_entry) + ABSOLUTE(startup_xen); +#endif +xen_elfnote_hypercall_page_value = + ABSOLUTE(xen_elfnote_hypercall_page) + ABSOLUTE(hypercall_page); +#endif +#ifdef CONFIG_PVH +xen_elfnote_phys32_entry_value = + 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 7ca51a4da2179..e6f39d77f0b48 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) -SYM_CODE_START_LOCAL(pvh_start_xen) +SYM_CODE_START(pvh_start_xen) UNWIND_HINT_END_OF_STACK cld @@ -300,5 +300,5 @@ SYM_DATA_END(pvh_level2_kernel_pgt) .long KERNEL_IMAGE_SIZE - 1) #endif - 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_value - .) diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index c101bed619400..3ede19ca8432c 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] = { [S_ABS] = "^(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 758bcd47b72d3..7f6c69dbb8165 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_value - .) ELFNOTE(Xen, XEN_ELFNOTE_FEATURES, .ascii "!writable_page_tables") ELFNOTE(Xen, XEN_ELFNOTE_PAE_MODE, .asciz "yes") ELFNOTE(Xen, XEN_ELFNOTE_L1_MFN_VALID, @@ -115,7 +116,8 @@ SYM_CODE_END(xen_cpu_bringup_again) #else # define FEATURES_DOM0 0 #endif - ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, _ASM_PTR hypercall_page) + ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, .globl xen_elfnote_hypercall_page; + xen_elfnote_hypercall_page: _ASM_PTR xen_elfnote_hypercall_page_value - .) ELFNOTE(Xen, XEN_ELFNOTE_SUPPORTED_FEATURES, .long FEATURES_PV | FEATURES_PVH | FEATURES_DOM0) ELFNOTE(Xen, XEN_ELFNOTE_LOADER, .asciz "generic")