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x86/pti: Map the vsyscall page if needed
Make VSYSCALLs work fully in PTI mode by mapping them properly to the user space visible page tables. [ tglx: Hide unused functions (Patch by Arnd Bergmann) ] Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Laight <David.Laight@aculab.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
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parent
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commit
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3 changed files with 69 additions and 3 deletions
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@ -344,14 +344,14 @@ int in_gate_area_no_mm(unsigned long addr)
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* vsyscalls but leave the page not present. If so, we skip calling
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* this.
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*/
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static void __init set_vsyscall_pgtable_user_bits(void)
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void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
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{
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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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pmd_t *pmd;
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pgd = pgd_offset_k(VSYSCALL_ADDR);
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pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);
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set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
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p4d = p4d_offset(pgd, VSYSCALL_ADDR);
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#if CONFIG_PGTABLE_LEVELS >= 5
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@ -373,7 +373,7 @@ void __init map_vsyscall(void)
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vsyscall_mode == NATIVE
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? PAGE_KERNEL_VSYSCALL
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: PAGE_KERNEL_VVAR);
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set_vsyscall_pgtable_user_bits();
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set_vsyscall_pgtable_user_bits(swapper_pg_dir);
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}
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BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
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@ -7,6 +7,7 @@
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#ifdef CONFIG_X86_VSYSCALL_EMULATION
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extern void map_vsyscall(void);
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extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
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/*
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* Called on instruction fetch fault in vsyscall page.
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@ -38,6 +38,7 @@
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#include <asm/cpufeature.h>
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#include <asm/hypervisor.h>
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#include <asm/vsyscall.h>
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#include <asm/cmdline.h>
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#include <asm/pti.h>
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#include <asm/pgtable.h>
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@ -223,6 +224,69 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
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return pmd_offset(pud, address);
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}
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#ifdef CONFIG_X86_VSYSCALL_EMULATION
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/*
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* Walk the shadow copy of the page tables (optionally) trying to allocate
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* page table pages on the way down. Does not support large pages.
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*
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* Note: this is only used when mapping *new* kernel data into the
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* user/shadow page tables. It is never used for userspace data.
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*
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* Returns a pointer to a PTE on success, or NULL on failure.
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*/
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static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address)
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{
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gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
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pmd_t *pmd = pti_user_pagetable_walk_pmd(address);
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pte_t *pte;
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/* We can't do anything sensible if we hit a large mapping. */
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if (pmd_large(*pmd)) {
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WARN_ON(1);
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return NULL;
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}
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if (pmd_none(*pmd)) {
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unsigned long new_pte_page = __get_free_page(gfp);
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if (!new_pte_page)
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return NULL;
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if (pmd_none(*pmd)) {
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set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page)));
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new_pte_page = 0;
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}
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if (new_pte_page)
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free_page(new_pte_page);
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}
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pte = pte_offset_kernel(pmd, address);
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if (pte_flags(*pte) & _PAGE_USER) {
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WARN_ONCE(1, "attempt to walk to user pte\n");
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return NULL;
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}
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return pte;
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}
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static void __init pti_setup_vsyscall(void)
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{
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pte_t *pte, *target_pte;
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unsigned int level;
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pte = lookup_address(VSYSCALL_ADDR, &level);
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if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte))
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return;
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target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR);
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if (WARN_ON(!target_pte))
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return;
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*target_pte = *pte;
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set_vsyscall_pgtable_user_bits(kernel_to_user_pgdp(swapper_pg_dir));
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}
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#else
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static void __init pti_setup_vsyscall(void) { }
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#endif
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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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@ -319,4 +383,5 @@ void __init pti_init(void)
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pti_clone_user_shared();
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pti_clone_entry_text();
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pti_setup_espfix64();
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pti_setup_vsyscall();
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}
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