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x86/mm/pti: Add functions to clone kernel PMDs
Provide infrastructure to: - find a kernel PMD for a mapping which must be visible to user space for the entry/exit code to work. - walk an address range and share the kernel PMD with it. This reuses a small part of the original KAISER patches to populate the user space page table. [ tglx: Made it universally usable so it can be used for any kind of shared mapping. Add a mechanism to clear specific bits in the user space visible PMD entry. Folded Andys simplifactions ] Originally-by: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Borislav Petkov <bpetkov@suse.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Laight <David.Laight@aculab.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Eduardo Valentin <eduval@amazon.com> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com> Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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1 changed files with 127 additions and 0 deletions
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@ -48,6 +48,11 @@
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#undef pr_fmt
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#define pr_fmt(fmt) "Kernel/User page tables isolation: " fmt
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/* Backporting helper */
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#ifndef __GFP_NOTRACK
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#define __GFP_NOTRACK 0
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#endif
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static void __init pti_print_if_insecure(const char *reason)
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{
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if (boot_cpu_has_bug(X86_BUG_CPU_INSECURE))
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@ -137,6 +142,128 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pgd_t pgd)
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return pgd;
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}
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/*
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* Walk the user copy of the page tables (optionally) trying to allocate
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* page table pages on the way down.
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*
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* Returns a pointer to a P4D on success, or NULL on failure.
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*/
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static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
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{
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pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address));
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gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
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if (address < PAGE_OFFSET) {
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WARN_ONCE(1, "attempt to walk user address\n");
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return NULL;
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}
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if (pgd_none(*pgd)) {
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unsigned long new_p4d_page = __get_free_page(gfp);
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if (!new_p4d_page)
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return NULL;
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if (pgd_none(*pgd)) {
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set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));
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new_p4d_page = 0;
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}
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if (new_p4d_page)
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free_page(new_p4d_page);
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}
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BUILD_BUG_ON(pgd_large(*pgd) != 0);
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return p4d_offset(pgd, address);
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}
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/*
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* Walk the user copy of the page tables (optionally) trying to allocate
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* page table pages on the way down.
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*
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* Returns a pointer to a PMD on success, or NULL on failure.
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*/
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static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
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{
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gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
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p4d_t *p4d = pti_user_pagetable_walk_p4d(address);
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pud_t *pud;
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BUILD_BUG_ON(p4d_large(*p4d) != 0);
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if (p4d_none(*p4d)) {
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unsigned long new_pud_page = __get_free_page(gfp);
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if (!new_pud_page)
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return NULL;
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if (p4d_none(*p4d)) {
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set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
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new_pud_page = 0;
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}
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if (new_pud_page)
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free_page(new_pud_page);
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}
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pud = pud_offset(p4d, address);
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/* The user page tables do not use large mappings: */
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if (pud_large(*pud)) {
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WARN_ON(1);
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return NULL;
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}
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if (pud_none(*pud)) {
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unsigned long new_pmd_page = __get_free_page(gfp);
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if (!new_pmd_page)
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return NULL;
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if (pud_none(*pud)) {
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set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
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new_pmd_page = 0;
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}
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if (new_pmd_page)
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free_page(new_pmd_page);
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}
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return pmd_offset(pud, address);
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}
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static void __init
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pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
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{
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unsigned long addr;
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/*
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* Clone the populated PMDs which cover start to end. These PMD areas
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* can have holes.
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*/
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for (addr = start; addr < end; addr += PMD_SIZE) {
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pmd_t *pmd, *target_pmd;
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pgd_t *pgd;
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p4d_t *p4d;
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pud_t *pud;
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pgd = pgd_offset_k(addr);
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if (WARN_ON(pgd_none(*pgd)))
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return;
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p4d = p4d_offset(pgd, addr);
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if (WARN_ON(p4d_none(*p4d)))
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return;
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pud = pud_offset(p4d, addr);
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if (pud_none(*pud))
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continue;
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pmd = pmd_offset(pud, addr);
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if (pmd_none(*pmd))
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continue;
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target_pmd = pti_user_pagetable_walk_pmd(addr);
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if (WARN_ON(!target_pmd))
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return;
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/*
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* Copy the PMD. That is, the kernelmode and usermode
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* tables will share the last-level page tables of this
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* address range
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*/
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*target_pmd = pmd_clear_flags(*pmd, clear);
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}
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}
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/*
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* Initialize kernel page table isolation
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*/
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