| Message ID | 20170410164420.64003-4-thgarnie@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Apr 10, 2017 at 09:44:20AM -0700, Thomas Garnier wrote: > Disable the generic pre-usermode check in favor of an optimized > implementation. This patch adds specific checks on user-mode return path > to make it faster and smaller. > > The address limit is checked on each syscall return path to user-mode. > If it was changed, a generic handler is called to stop the kernel on an > explicit check. > > Signed-off-by: Thomas Garnier <thgarnie@google.com> > --- > Based on next-20170410 > --- > arch/arm64/Kconfig | 1 + > arch/arm64/kernel/entry.S | 13 +++++++++++++ > 2 files changed, 14 insertions(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 9b8fcab7da56..3f9e8e7d9376 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -24,6 +24,7 @@ config ARM64 > select ARCH_WANT_COMPAT_IPC_PARSE_VERSION > select ARCH_WANT_FRAME_POINTERS > select ARCH_HAS_UBSAN_SANITIZE_ALL > + select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE > select ARM_AMBA > select ARM_ARCH_TIMER > select ARM_GIC > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 43512d4d7df2..bdd094c7837a 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -744,6 +744,8 @@ ENDPROC(cpu_switch_to) > ret_fast_syscall: > disable_irq // disable interrupts > str x0, [sp, #S_X0] // returned x0 > + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change > + tbnz x2, #63, addr_limit_fail > ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing > and x2, x1, #_TIF_SYSCALL_WORK > cbnz x2, ret_fast_syscall_trace > @@ -771,6 +773,9 @@ work_pending: > */ > ret_to_user: > disable_irq // disable interrupts > + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change > + tbnz x2, #63, addr_limit_fail > + Nitpick: unnecessary empty line added. > ldr x1, [tsk, #TSK_TI_FLAGS] > and x2, x1, #_TIF_WORK_MASK > cbnz x2, work_pending > @@ -780,6 +785,14 @@ finish_ret_to_user: > ENDPROC(ret_to_user) > > /* > + * Address limit was incorrect before returning in user-mode which could be > + * used to elevate privileges. Call the generic handler to stop the kernel on > + * the appropriate check. This function does not return. > + */ > +addr_limit_fail: > + bl address_limit_check_failed You could do a "b address_limit_check_failed" rather than "bl" since we don't care about returning here (and a nitpick: insert tab between "b" and "address_limit_check_failed"). With the above: Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 9b8fcab7da56..3f9e8e7d9376 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -24,6 +24,7 @@ config ARM64 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION select ARCH_WANT_FRAME_POINTERS select ARCH_HAS_UBSAN_SANITIZE_ALL + select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE select ARM_AMBA select ARM_ARCH_TIMER select ARM_GIC diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 43512d4d7df2..bdd094c7837a 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -744,6 +744,8 @@ ENDPROC(cpu_switch_to) ret_fast_syscall: disable_irq // disable interrupts str x0, [sp, #S_X0] // returned x0 + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change + tbnz x2, #63, addr_limit_fail ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for syscall tracing and x2, x1, #_TIF_SYSCALL_WORK cbnz x2, ret_fast_syscall_trace @@ -771,6 +773,9 @@ work_pending: */ ret_to_user: disable_irq // disable interrupts + ldr x2, [tsk, #TSK_TI_ADDR_LIMIT] // check addr limit change + tbnz x2, #63, addr_limit_fail + ldr x1, [tsk, #TSK_TI_FLAGS] and x2, x1, #_TIF_WORK_MASK cbnz x2, work_pending @@ -780,6 +785,14 @@ finish_ret_to_user: ENDPROC(ret_to_user) /* + * Address limit was incorrect before returning in user-mode which could be + * used to elevate privileges. Call the generic handler to stop the kernel on + * the appropriate check. This function does not return. + */ +addr_limit_fail: + bl address_limit_check_failed + +/* * This is how we return from a fork. */ ENTRY(ret_from_fork)
Disable the generic pre-usermode check in favor of an optimized implementation. This patch adds specific checks on user-mode return path to make it faster and smaller. The address limit is checked on each syscall return path to user-mode. If it was changed, a generic handler is called to stop the kernel on an explicit check. Signed-off-by: Thomas Garnier <thgarnie@google.com> --- Based on next-20170410 --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/entry.S | 13 +++++++++++++ 2 files changed, 14 insertions(+)