# git rev-parse -q --verify dc8b1290efbbe974d9968106a03077823d0863d6^{commit} dc8b1290efbbe974d9968106a03077823d0863d6 already have revision, skipping fetch # git checkout -q -f -B kisskb dc8b1290efbbe974d9968106a03077823d0863d6 # git clean -qxdf # < git log -1 # commit dc8b1290efbbe974d9968106a03077823d0863d6 # Author: Russell Currey # Date: Fri Mar 1 01:49:17 2019 +1100 # # powerpc/64s: Implement KUAP for Radix MMU # # Kernel Userspace Access Prevention utilises a feature of the Radix MMU # which disallows read and write access to userspace addresses. By # utilising this, the kernel is prevented from accessing user data from # outside of trusted paths that perform proper safety checks, such as # copy_{to/from}_user() and friends. # # Userspace access is disabled from early boot and is only enabled when # performing an operation like copy_{to/from}_user(). The register that # controls this (AMR) does not prevent userspace from accessing itself, # so there is no need to save and restore when entering and exiting # userspace. # # This feature has a slight performance impact which I roughly measured # to be 3% slower in the worst case (performing 1GB of 1 byte # read()/write() syscalls), and is gated behind the CONFIG_PPC_KUAP # option for performance-critical builds. # # This feature can be tested by using the lkdtm driver (CONFIG_LKDTM=y) # and performing the following: # # # (echo ACCESS_USERSPACE) > [debugfs]/provoke-crash/DIRECT # # If enabled, this should send SIGSEGV to the thread. # # mpe: # - Drop the unused paca flags. # - Zero the UAMOR to be safe. # - Save the AMR when we enter the kernel from the kernel and then # block user access again if it's not already blocked. # - Restore on the way back to the kernel. # - This means we handle nesting of interrupts properly, ie. we are # protected inside the page fault handler caused by a user access. # - Add paranoid checking of AMR in switch and syscall return. # - Add isync()'s around AMR writes as per the ISA. # - Support selectively disabling read or write, with no support for # nesting. # # Co-authored-by: Michael Ellerman # Signed-off-by: Russell Currey # Signed-off-by: Michael Ellerman # --- # # v5: # - On kernel entry check if the AMR is already blocking user access # and if so don't do the mtspr again (pointed out by Nick). # - Rework the constants to make the asm a bit cleaner and avoid any # hard coded shifts. # - Selectively disable read or write, we don't support nesting and # shouldn't need to (famous last words). # < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-gcc --version # < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-ld --version # < git log --format=%s --max-count=1 dc8b1290efbbe974d9968106a03077823d0863d6 # < make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_ppc64e_defconfig_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- ppc64e_defconfig # make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_ppc64e_defconfig_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux- /kisskb/src/kernel/cgroup/cgroup-v1.c: In function 'cgroup1_mount': /kisskb/src/kernel/cgroup/cgroup-v1.c:1263:20: warning: 'root' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl': /kisskb/src/kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/kernel/trace/trace_dynevent.c: In function 'create_dyn_event': /kisskb/src/kernel/trace/trace_dynevent.c:89:5: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/tty/serial/8250/8250_core.c: In function 'univ8250_release_irq': /kisskb/src/drivers/tty/serial/8250/8250_core.c:247:18: warning: 'i' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/tty/serial/8250/8250_core.c:227:19: note: 'i' was declared here /kisskb/src/net/bridge/br_netlink.c: In function 'br_afspec.isra.28': /kisskb/src/net/bridge/br_netlink.c:652:7: warning: 'err' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c: In function 'proc_reg_open': /kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c:339:21: note: 'pdeo' was declared here /kisskb/src/fs/nfsd/nfs4xdr.c: In function 'nfsd4_encode_components_esc': /kisskb/src/fs/nfsd/nfs4xdr.c:2076:9: warning: 'str' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/net/tun.c: In function 'tun_get_user': /kisskb/src/drivers/net/tun.c:1843:30: warning: 'copylen' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/net/tun.c:1753:46: warning: 'linear' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/udf/unicode.c: In function 'udf_name_conv_char': /kisskb/src/fs/udf/unicode.c:132:8: warning: 'c' may be used uninitialized in this function [-Wuninitialized] WARNING: vmlinux.o (.PPC.EMB.apuinfo): unexpected non-allocatable section. Did you forget to use "ax"/"aw" in a .S file? Note that for example contains section definitions for use in .S files. WARNING: modpost: Found 1 section mismatch(es). To see full details build your kernel with: 'make CONFIG_DEBUG_SECTION_MISMATCH=y' INFO: Uncompressed kernel (size 0xc2a830) overlaps the address of the wrapper(0x400000) INFO: Fixing the link_address of wrapper to (0xd00000) Image Name: Linux-5.0.0-rc2-gdc8b1290efbb Created: Sat Mar 2 21:30:07 2019 Image Type: PowerPC Linux Kernel Image (gzip compressed) Data Size: 5207089 Bytes = 5085.05 KiB = 4.97 MiB Load Address: 00000000 Entry Point: 00000000 Completed OK # rm -rf /kisskb/build/powerpc-next_ppc64e_defconfig_powerpc-gcc4.6 # Build took: 0:01:25.790837