4.14-stable review patch. If anyone has any objections, please let me know.
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From: Andy Lutomirski luto@kernel.org
commit 85900ea51577e31b186e523c8f4e068c79ecc7d3 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/entry/vsyscall/vsyscall_64.c | 6 +-- arch/x86/include/asm/vsyscall.h | 1 arch/x86/mm/pti.c | 65 ++++++++++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 3 deletions(-)
--- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -344,14 +344,14 @@ int in_gate_area_no_mm(unsigned long add * vsyscalls but leave the page not present. If so, we skip calling * this. */ -static void __init set_vsyscall_pgtable_user_bits(void) +void __init set_vsyscall_pgtable_user_bits(pgd_t *root) { pgd_t *pgd; p4d_t *p4d; pud_t *pud; pmd_t *pmd;
- pgd = pgd_offset_k(VSYSCALL_ADDR); + pgd = pgd_offset_pgd(root, VSYSCALL_ADDR); set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER)); p4d = p4d_offset(pgd, VSYSCALL_ADDR); #if CONFIG_PGTABLE_LEVELS >= 5 @@ -373,7 +373,7 @@ void __init map_vsyscall(void) vsyscall_mode == NATIVE ? PAGE_KERNEL_VSYSCALL : PAGE_KERNEL_VVAR); - set_vsyscall_pgtable_user_bits(); + set_vsyscall_pgtable_user_bits(swapper_pg_dir); }
BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != --- a/arch/x86/include/asm/vsyscall.h +++ b/arch/x86/include/asm/vsyscall.h @@ -7,6 +7,7 @@
#ifdef CONFIG_X86_VSYSCALL_EMULATION extern void map_vsyscall(void); +extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
/* * Called on instruction fetch fault in vsyscall page. --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -38,6 +38,7 @@
#include <asm/cpufeature.h> #include <asm/hypervisor.h> +#include <asm/vsyscall.h> #include <asm/cmdline.h> #include <asm/pti.h> #include <asm/pgtable.h> @@ -223,6 +224,69 @@ static pmd_t *pti_user_pagetable_walk_pm return pmd_offset(pud, address); }
+#ifdef CONFIG_X86_VSYSCALL_EMULATION +/* + * Walk the shadow copy of the page tables (optionally) trying to allocate + * page table pages on the way down. Does not support large pages. + * + * Note: this is only used when mapping *new* kernel data into the + * user/shadow page tables. It is never used for userspace data. + * + * Returns a pointer to a PTE on success, or NULL on failure. + */ +static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address) +{ + gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); + pmd_t *pmd = pti_user_pagetable_walk_pmd(address); + pte_t *pte; + + /* We can't do anything sensible if we hit a large mapping. */ + if (pmd_large(*pmd)) { + WARN_ON(1); + return NULL; + } + + if (pmd_none(*pmd)) { + unsigned long new_pte_page = __get_free_page(gfp); + if (!new_pte_page) + return NULL; + + if (pmd_none(*pmd)) { + set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page))); + new_pte_page = 0; + } + if (new_pte_page) + free_page(new_pte_page); + } + + pte = pte_offset_kernel(pmd, address); + if (pte_flags(*pte) & _PAGE_USER) { + WARN_ONCE(1, "attempt to walk to user pte\n"); + return NULL; + } + return pte; +} + +static void __init pti_setup_vsyscall(void) +{ + pte_t *pte, *target_pte; + unsigned int level; + + pte = lookup_address(VSYSCALL_ADDR, &level); + if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte)) + return; + + target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR); + if (WARN_ON(!target_pte)) + return; + + *target_pte = *pte; + set_vsyscall_pgtable_user_bits(kernel_to_user_pgdp(swapper_pg_dir)); +} +#else +static void __init pti_setup_vsyscall(void) { } +#endif + static void __init pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear) { @@ -319,4 +383,5 @@ void __init pti_init(void) pti_clone_user_shared(); pti_clone_entry_text(); pti_setup_espfix64(); + pti_setup_vsyscall(); }