Messages in this thread Patch in this message | | | Date | Sat, 16 Dec 2017 22:23:56 +0100 | From | Thomas Gleixner <> | Subject | [patch V149 02/50] x86/vsyscall/64: Explicitly set _PAGE_USER in the pagetable hierarchy |
| |
From: Andy Lutomirski <luto@kernel.org>
The kernel is very erratic as to which pagetables have _PAGE_USER set. The vsyscall page gets lucky: it seems that all of the relevant pagetables are among the apparently arbitrary ones that set _PAGE_USER. Rather than relying on chance, just explicitly set _PAGE_USER.
This will let us clean up pagetable setup to stop setting _PAGE_USER. The added code can also be reused by pagetable isolation to manage the _PAGE_USER bit in the usermode tables.
Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: David Laight <David.Laight@aculab.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> --- arch/x86/entry/vsyscall/vsyscall_64.c | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-)
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index f279ba2643dc..bc88a0540347 100644 --- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -329,16 +329,47 @@ int in_gate_area_no_mm(unsigned long addr) return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR; } +/* + * The VSYSCALL page is the only user-accessible page in the kernel address + * range. Normally, the kernel page tables can have _PAGE_USER clear, but + * the tables covering VSYSCALL_ADDR need _PAGE_USER set if vsyscalls + * are enabled. + * + * Some day we may create a "minimal" vsyscall mode in which we emulate + * vsyscalls but leave the page not present. If so, we skip calling + * this. + */ +static void __init set_vsyscall_pgtable_user_bits(void) +{ + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + + pgd = pgd_offset_k(VSYSCALL_ADDR); + pgd->pgd |= _PAGE_USER; + p4d = p4d_offset(pgd, VSYSCALL_ADDR); +#if CONFIG_PGTABLE_LEVELS >= 5 + p4d->p4d |= _PAGE_USER; +#endif + pud = pud_offset(p4d, VSYSCALL_ADDR); + pud->pud |= _PAGE_USER; + pmd = pmd_offset(pud, VSYSCALL_ADDR); + pmd->pmd |= _PAGE_USER; +} + void __init map_vsyscall(void) { extern char __vsyscall_page; unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page); - if (vsyscall_mode != NONE) + if (vsyscall_mode != NONE) { __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall, vsyscall_mode == NATIVE ? PAGE_KERNEL_VSYSCALL : PAGE_KERNEL_VVAR); + set_vsyscall_pgtable_user_bits(); + } BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) != (unsigned long)VSYSCALL_ADDR); -- 2.14.1
| |