From: Dave Hansen <[email protected]> The KERNEL_PAGE_TABLE_ISOLATION code attempts to "poison" the user portion of the kernel page tables. It detects entries that it wants that it wants to poison in two ways:
* Looking for addresses >= PAGE_OFFSET * Looking for entries without _PAGE_USER set But, to allow the _PAGE_USER check to work, it must never be set on init_mm entries, and an earlier patch in this series ensured that it will never be set. The VDSO is at a address >= PAGE_OFFSET and it is also mapped by init_mm. Because of the earlier, KERNEL_PAGE_TABLE_ISOLATION-enforced restriction, _PAGE_USER is never set which makes the VDSO unreadable to userspace. This makes the "NATIVE" case totally unusable since userspace can not even see the memory any more. Disable it whenever KERNEL_PAGE_TABLE_ISOLATION is enabled. Also add some help text about how KERNEL_PAGE_TABLE_ISOLATION might affect the emulation case as well. Signed-off-by: Dave Hansen <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: Rik van Riel <[email protected]> Cc: [email protected] Cc: Denys Vlasenko <[email protected]> Cc: [email protected] Cc: [email protected] Cc: Peter Zijlstra <[email protected]> Cc: Brian Gerst <[email protected]> Cc: [email protected] Cc: [email protected] Cc: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: [email protected] Cc: Linus Torvalds <[email protected]> Cc: [email protected] Link: https://lkml.kernel.org/r/[email protected] --- arch/x86/Kconfig | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2249,6 +2249,9 @@ choice config LEGACY_VSYSCALL_NATIVE bool "Native" + # The VSYSCALL page comes from the kernel page tables + # and is not available when KERNEL_PAGE_TABLE_ISOLATION is enabled. + depends on !KERNEL_PAGE_TABLE_ISOLATION help Actual executable code is located in the fixed vsyscall address mapping, implementing time() efficiently. Since @@ -2266,6 +2269,11 @@ choice exploits. This configuration is recommended when userspace still uses the vsyscall area. + When KERNEL_PAGE_TABLE_ISOLATION is enabled, the vsyscall area will become + unreadable. This emulation option still works, but KERNEL_PAGE_TABLE_ISOLATION + will make it harder to do things like trace code using the + emulation. + config LEGACY_VSYSCALL_NONE bool "None" help
