This is a note to let you know that I've just added the patch titled powerpc/uaccess: Evaluate macro arguments once, before user access is allowed to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: powerpc-uaccess-evaluate-macro-arguments-once-before-user-access-is-allowed.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@xxxxxxxxxxxxxxx> know about it. >From foo@baz Fri Nov 20 08:28:41 AM CET 2020 From: Daniel Axtens <dja@xxxxxxxxxx> Date: Fri, 20 Nov 2020 11:07:03 +1100 Subject: powerpc/uaccess: Evaluate macro arguments once, before user access is allowed To: stable@xxxxxxxxxxxxxxx Cc: dja@xxxxxxxxxx Message-ID: <20201120000704.374811-8-dja@xxxxxxxxxx> From: Nicholas Piggin <npiggin@xxxxxxxxx> commit d02f6b7dab8228487268298ea1f21081c0b4b3eb upstream. get/put_user() can be called with nontrivial arguments. fs/proc/page.c has a good example: if (put_user(stable_page_flags(ppage), out)) { stable_page_flags() is quite a lot of code, including spin locks in the page allocator. Ensure these arguments are evaluated before user access is allowed. This improves security by reducing code with access to userspace, but it also fixes a PREEMPT bug with KUAP on powerpc/64s: stable_page_flags() is currently called with AMR set to allow writes, it ends up calling spin_unlock(), which can call preempt_schedule. But the task switch code can not be called with AMR set (it relies on interrupts saving the register), so this blows up. It's fine if the code inside allow_user_access() is preemptible, because a timer or IPI will save the AMR, but it's not okay to explicitly cause a reschedule. Fixes: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection") Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20200407041245.600651-1-npiggin@xxxxxxxxx Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/include/asm/uaccess.h | 49 ++++++++++++++++++++++++++----------- 1 file changed, 35 insertions(+), 14 deletions(-) --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -190,13 +190,17 @@ do { \ ({ \ long __pu_err; \ __typeof__(*(ptr)) __user *__pu_addr = (ptr); \ + __typeof__(*(ptr)) __pu_val = (x); \ + __typeof__(size) __pu_size = (size); \ + \ if (!is_kernel_addr((unsigned long)__pu_addr)) \ might_fault(); \ - __chk_user_ptr(ptr); \ + __chk_user_ptr(__pu_addr); \ if (do_allow) \ - __put_user_size((x), __pu_addr, (size), __pu_err); \ + __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ else \ - __put_user_size_allowed((x), __pu_addr, (size), __pu_err); \ + __put_user_size_allowed(__pu_val, __pu_addr, __pu_size, __pu_err); \ + \ __pu_err; \ }) @@ -204,9 +208,13 @@ do { \ ({ \ long __pu_err = -EFAULT; \ __typeof__(*(ptr)) __user *__pu_addr = (ptr); \ + __typeof__(*(ptr)) __pu_val = (x); \ + __typeof__(size) __pu_size = (size); \ + \ might_fault(); \ - if (access_ok(VERIFY_WRITE, __pu_addr, size)) \ - __put_user_size((x), __pu_addr, (size), __pu_err); \ + if (access_ok(VERIFY_WRITE, __pu_addr, __pu_size)) \ + __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ + \ __pu_err; \ }) @@ -214,8 +222,12 @@ do { \ ({ \ long __pu_err; \ __typeof__(*(ptr)) __user *__pu_addr = (ptr); \ - __chk_user_ptr(ptr); \ - __put_user_size((x), __pu_addr, (size), __pu_err); \ + __typeof__(*(ptr)) __pu_val = (x); \ + __typeof__(size) __pu_size = (size); \ + \ + __chk_user_ptr(__pu_addr); \ + __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ + \ __pu_err; \ }) @@ -289,15 +301,18 @@ do { \ long __gu_err; \ unsigned long __gu_val; \ __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ - __chk_user_ptr(ptr); \ + __typeof__(size) __gu_size = (size); \ + \ + __chk_user_ptr(__gu_addr); \ if (!is_kernel_addr((unsigned long)__gu_addr)) \ might_fault(); \ barrier_nospec(); \ if (do_allow) \ - __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \ + __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \ else \ - __get_user_size_allowed(__gu_val, __gu_addr, (size), __gu_err); \ + __get_user_size_allowed(__gu_val, __gu_addr, __gu_size, __gu_err); \ (x) = (__typeof__(*(ptr)))__gu_val; \ + \ __gu_err; \ }) @@ -322,12 +337,15 @@ do { \ long __gu_err = -EFAULT; \ unsigned long __gu_val = 0; \ __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ + __typeof__(size) __gu_size = (size); \ + \ might_fault(); \ - if (access_ok(VERIFY_READ, __gu_addr, (size))) { \ + if (access_ok(VERIFY_READ, __gu_addr, __gu_size)) { \ barrier_nospec(); \ - __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \ + __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \ } \ (x) = (__force __typeof__(*(ptr)))__gu_val; \ + \ __gu_err; \ }) @@ -336,10 +354,13 @@ do { \ long __gu_err; \ unsigned long __gu_val; \ __typeof__(*(ptr)) __user *__gu_addr = (ptr); \ - __chk_user_ptr(ptr); \ + __typeof__(size) __gu_size = (size); \ + \ + __chk_user_ptr(__gu_addr); \ barrier_nospec(); \ - __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \ + __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \ (x) = (__force __typeof__(*(ptr)))__gu_val; \ + \ __gu_err; \ }) Patches currently in stable-queue which might be from dja@xxxxxxxxxx are queue-4.4/powerpc-add-a-framework-for-user-access-tracking.patch queue-4.4/powerpc-implement-user_access_begin-and-friends.patch queue-4.4/powerpc-uaccess-evaluate-macro-arguments-once-before-user-access-is-allowed.patch queue-4.4/powerpc-64s-flush-l1d-after-user-accesses.patch queue-4.4/powerpc-64s-move-some-exception-handlers-out-of-line.patch queue-4.4/powerpc-64s-flush-l1d-on-kernel-entry.patch queue-4.4/powerpc-fix-__clear_user-with-kuap-enabled.patch queue-4.4/powerpc-64s-define-maskable_relon_exception_pseries_ool.patch