Tighten mapping protections on preloaded files on amd64.
- We load the kernel at 0x200000. Memory below that address need not be executable, so do not map it as such. - Remove references to .ldata and related sections in the kernel linker script. They come from ld.bfd's default linker script, but are not used, and we now use ld.lld to link the amd64 kernel. lld does not contain a default linker script. - Pad the .bss to a 2MB as we do between .text and .data. This forces the loader to load additional files starting in the following 2MB page, preserving the use of superpage mappings for kernel data. - Map memory above the kernel image with NX. The kernel linker now upgrades protections as needed, and other preloaded file types (e.g., entropy, microcode) need not be mapped with execute permissions in the first place. Reviewed by: kib MFC after: 1 month Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D21859
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=353731
@ -1422,22 +1422,22 @@ nkpt_init(vm_paddr_t addr)
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*
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*
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* This function operates on 2M pages, since we map the kernel space that
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* This function operates on 2M pages, since we map the kernel space that
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* way.
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* way.
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*
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* Note that this doesn't currently provide any protection for modules.
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*/
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*/
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static inline pt_entry_t
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static inline pt_entry_t
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bootaddr_rwx(vm_paddr_t pa)
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bootaddr_rwx(vm_paddr_t pa)
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{
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{
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/*
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/*
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* Everything in the same 2M page as the start of the kernel
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* The kernel is loaded at a 2MB-aligned address, and memory below that
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* should be static. On the other hand, things in the same 2M
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* need not be executable. The .bss section is padded to a 2MB
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* page as the end of the kernel could be read-write/executable,
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* boundary, so memory following the kernel need not be executable
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* as the kernel image is not guaranteed to end on a 2M boundary.
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* either. Preloaded kernel modules have their mapping permissions
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* fixed up by the linker.
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*/
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*/
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if (pa < trunc_2mpage(btext - KERNBASE) ||
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if (pa < trunc_2mpage(btext - KERNBASE) ||
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pa >= trunc_2mpage(_end - KERNBASE))
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pa >= trunc_2mpage(_end - KERNBASE))
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return (X86_PG_RW);
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return (X86_PG_RW | pg_nx);
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/*
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/*
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* The linker should ensure that the read-only and read-write
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* The linker should ensure that the read-only and read-write
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* portions don't share the same 2M page, so this shouldn't
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* portions don't share the same 2M page, so this shouldn't
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@ -1446,6 +1446,7 @@ bootaddr_rwx(vm_paddr_t pa)
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*/
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*/
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if (pa >= trunc_2mpage(brwsection - KERNBASE))
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if (pa >= trunc_2mpage(brwsection - KERNBASE))
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return (X86_PG_RW | pg_nx);
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return (X86_PG_RW | pg_nx);
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/*
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/*
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* Mark any 2M page containing kernel text as read-only. Mark
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* Mark any 2M page containing kernel text as read-only. Mark
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* other pages with read-only data as read-only and not executable.
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* other pages with read-only data as read-only and not executable.
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@ -45,12 +45,6 @@ SECTIONS
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.rela.got : { *(.rela.got) }
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.rela.got : { *(.rela.got) }
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.rel.bss : { *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*) }
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.rel.bss : { *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*) }
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.rela.bss : { *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) }
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.rela.bss : { *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) }
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.rel.ldata : { *(.rel.ldata .rel.ldata.* .rel.gnu.linkonce.l.*) }
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.rela.ldata : { *(.rela.ldata .rela.ldata.* .rela.gnu.linkonce.l.*) }
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.rel.lbss : { *(.rel.lbss .rel.lbss.* .rel.gnu.linkonce.lb.*) }
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.rela.lbss : { *(.rela.lbss .rela.lbss.* .rela.gnu.linkonce.lb.*) }
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.rel.lrodata : { *(.rel.lrodata .rel.lrodata.* .rel.gnu.linkonce.lr.*) }
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.rela.lrodata : { *(.rela.lrodata .rela.lrodata.* .rela.gnu.linkonce.lr.*) }
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.rel.plt : { *(.rel.plt) }
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.rel.plt : { *(.rel.plt) }
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.rela.plt : { *(.rela.plt) }
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.rela.plt : { *(.rela.plt) }
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.init :
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.init :
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@ -179,30 +173,10 @@ SECTIONS
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*(.dynbss)
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*(.dynbss)
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*(.bss .bss.* .gnu.linkonce.b.*)
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*(.bss .bss.* .gnu.linkonce.b.*)
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*(COMMON)
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*(COMMON)
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/* Align here to ensure that the .bss section occupies space up to
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/* Ensure that the .bss section ends at a superpage boundary.
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_end. Align after .bss to ensure correct alignment even if the
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This way it can be mapped using non-executable large pages. */
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.bss section disappears because there are no input sections.
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. = ALIGN(0x200000);
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FIXME: Why do we need it? When there is no .bss section, we don't
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pad the .data section. */
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. = ALIGN(. != 0 ? 64 / 8 : 1);
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}
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}
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.lbss :
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{
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*(.dynlbss)
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*(.lbss .lbss.* .gnu.linkonce.lb.*)
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*(LARGE_COMMON)
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}
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. = ALIGN(64 / 8);
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.lrodata ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
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{
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*(.lrodata .lrodata.* .gnu.linkonce.lr.*)
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}
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.ldata ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
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{
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*(.ldata .ldata.* .gnu.linkonce.l.*)
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. = ALIGN(. != 0 ? 64 / 8 : 1);
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}
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. = ALIGN(64 / 8);
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_end = .; PROVIDE (end = .);
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_end = .; PROVIDE (end = .);
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. = DATA_SEGMENT_END (.);
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. = DATA_SEGMENT_END (.);
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/* Stabs debugging sections. */
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/* Stabs debugging sections. */
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