This is a note to let you know that I've just added the patch titled

Map the vsyscall page with _PAGE_USER

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: map-the-vsyscall-page-with-_page_user.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From: Borislav Petkov bp@suse.de Date: Thu, 4 Jan 2018 17:42:45 +0100 Subject: Map the vsyscall page with _PAGE_USER

From: Borislav Petkov bp@suse.de

This needs to happen early in kaiser_pagetable_walk(), before the hierarchy is established so that _PAGE_USER permission can be really set.

A proper fix would be to teach kaiser_pagetable_walk() to update those permissions but the vsyscall page is the only exception here so ...

Signed-off-by: Borislav Petkov bp@suse.de Acked-by: Hugh Dickins hughd@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/entry/vsyscall/vsyscall_64.c | 5 +++++ arch/x86/include/asm/vsyscall.h | 2 ++ arch/x86/mm/kaiser.c | 34 ++++++++++++++++++++++++++++++---- 3 files changed, 37 insertions(+), 4 deletions(-)

--- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -66,6 +66,11 @@ static int __init vsyscall_setup(char *s } early_param("vsyscall", vsyscall_setup);

+bool vsyscall_enabled(void) +{ + return vsyscall_mode != NONE; +} + static void warn_bad_vsyscall(const char *level, struct pt_regs *regs, const char *message) { --- a/arch/x86/include/asm/vsyscall.h +++ b/arch/x86/include/asm/vsyscall.h @@ -12,12 +12,14 @@ extern void map_vsyscall(void); * Returns true if handled. */ extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address); +extern bool vsyscall_enabled(void); #else static inline void map_vsyscall(void) {} static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address) { return false; } +bool vsyscall_enabled(void) { return false; } #endif

#endif /* _ASM_X86_VSYSCALL_H */ --- a/arch/x86/mm/kaiser.c +++ b/arch/x86/mm/kaiser.c @@ -20,6 +20,7 @@ #include <asm/pgalloc.h> #include <asm/desc.h> #include <asm/cmdline.h> +#include <asm/vsyscall.h>

int kaiser_enabled __read_mostly = 1; EXPORT_SYMBOL(kaiser_enabled); /* for inlined TLB flush functions */ @@ -111,12 +112,13 @@ static inline unsigned long get_pa_from_ * * Returns a pointer to a PTE on success, or NULL on failure. */ -static pte_t *kaiser_pagetable_walk(unsigned long address) +static pte_t *kaiser_pagetable_walk(unsigned long address, bool user) { pmd_t *pmd; pud_t *pud; pgd_t *pgd = native_get_shadow_pgd(pgd_offset_k(address)); gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); + unsigned long prot = _KERNPG_TABLE;

if (pgd_none(*pgd)) { WARN_ONCE(1, "All shadow pgds should have been populated"); @@ -124,6 +126,17 @@ static pte_t *kaiser_pagetable_walk(unsi } BUILD_BUG_ON(pgd_large(*pgd) != 0);

+ if (user) { + /* + * The vsyscall page is the only page that will have + * _PAGE_USER set. Catch everything else. + */ + BUG_ON(address != VSYSCALL_ADDR); + + set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER)); + prot = _PAGE_TABLE; + } + pud = pud_offset(pgd, address); /* The shadow page tables do not use large mappings: */ if (pud_large(*pud)) { @@ -136,7 +149,7 @@ static pte_t *kaiser_pagetable_walk(unsi return NULL; spin_lock(&shadow_table_allocation_lock); if (pud_none(*pud)) { - set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page))); + set_pud(pud, __pud(prot | __pa(new_pmd_page))); __inc_zone_page_state(virt_to_page((void *) new_pmd_page), NR_KAISERTABLE); } else @@ -156,7 +169,7 @@ static pte_t *kaiser_pagetable_walk(unsi return NULL; spin_lock(&shadow_table_allocation_lock); if (pmd_none(*pmd)) { - set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page))); + set_pmd(pmd, __pmd(prot | __pa(new_pte_page))); __inc_zone_page_state(virt_to_page((void *) new_pte_page), NR_KAISERTABLE); } else @@ -192,7 +205,7 @@ static int kaiser_add_user_map(const voi ret = -EIO; break; } - pte = kaiser_pagetable_walk(address); + pte = kaiser_pagetable_walk(address, flags & _PAGE_USER); if (!pte) { ret = -ENOMEM; break; @@ -319,6 +332,19 @@ void __init kaiser_init(void)

kaiser_init_all_pgds();

+ /* + * Note that this sets _PAGE_USER and it needs to happen when the + * pagetable hierarchy gets created, i.e., early. Otherwise + * kaiser_pagetable_walk() will encounter initialized PTEs in the + * hierarchy and not set the proper permissions, leading to the + * pagefaults with page-protection violations when trying to read the + * vsyscall page. For example. + */ + if (vsyscall_enabled()) + kaiser_add_user_map_early((void *)VSYSCALL_ADDR, + PAGE_SIZE, + __PAGE_KERNEL_VSYSCALL); + for_each_possible_cpu(cpu) { void *percpu_vaddr = __per_cpu_user_mapped_start + per_cpu_offset(cpu);

Patches currently in stable-queue which might be from bp@suse.de are

queue-4.4/map-the-vsyscall-page-with-_page_user.patch queue-4.4/x86-kasan-write-protect-kasan-zero-shadow.patch