* [PATCH v2 1/3] powerpc/mm/radix: Use KUEP API for Radix MMU
2018-12-10 7:00 [PATCH v2 0/3] [PATCH v2 0/3] Kernel Userspace Protection for Radix MMU Russell Currey
@ 2018-12-10 7:00 ` Russell Currey
2018-12-10 7:00 ` [PATCH v2 2/3] powerpc/lib: Refactor __patch_instruction() to use __put_user_asm() Russell Currey
2018-12-10 7:00 ` [PATCH v2 3/3] powerpc/64s: Implement KUAP for Radix MMU Russell Currey
2 siblings, 0 replies; 7+ messages in thread
From: Russell Currey @ 2018-12-10 7:00 UTC (permalink / raw)
To: linuxppc-dev
Cc: mikey, mpe, benh, npiggin, christophe.leroy, kernel-hardening,
Russell Currey
Execution protection already exists on radix, this just refactors
the radix init to provide the KUEP setup function instead.
Thus, the only functional change is that it can now be disabled.
Signed-off-by: Russell Currey <ruscur@russell.cc>
---
arch/powerpc/mm/pgtable-radix.c | 11 ++++++++---
arch/powerpc/platforms/Kconfig.cputype | 1 +
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 931156069a81..3565e266994b 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -535,8 +535,14 @@ static void radix_init_amor(void)
mtspr(SPRN_AMOR, (3ul << 62));
}
-static void radix_init_iamr(void)
+#ifdef CONFIG_PPC_KUEP
+void __init setup_kuep(bool disabled)
{
+ if (disabled || !early_radix_enabled())
+ return;
+
+ pr_warn("Activating Kernel Userspace Execution Prevention\n");
+
/*
* Radix always uses key0 of the IAMR to determine if an access is
* allowed. We set bit 0 (IBM bit 1) of key0, to prevent instruction
@@ -544,6 +550,7 @@ static void radix_init_iamr(void)
*/
mtspr(SPRN_IAMR, (1ul << 62));
}
+#endif
void __init radix__early_init_mmu(void)
{
@@ -605,7 +612,6 @@ void __init radix__early_init_mmu(void)
memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
- radix_init_iamr();
radix_init_pgtable();
/* Switch to the guard PID before turning on MMU */
radix__switch_mmu_context(NULL, &init_mm);
@@ -627,7 +633,6 @@ void radix__early_init_mmu_secondary(void)
__pa(partition_tb) | (PATB_SIZE_SHIFT - 12));
radix_init_amor();
}
- radix_init_iamr();
radix__switch_mmu_context(NULL, &init_mm);
if (cpu_has_feature(CPU_FTR_HVMODE))
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 9997b5ea5693..48cc8df0fdd2 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -335,6 +335,7 @@ config PPC_RADIX_MMU
bool "Radix MMU Support"
depends on PPC_BOOK3S_64
select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
+ select PPC_HAVE_KUEP
default y
help
Enable support for the Power ISA 3.0 Radix style MMU. Currently this
--
2.19.2
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v2 2/3] powerpc/lib: Refactor __patch_instruction() to use __put_user_asm()
2018-12-10 7:00 [PATCH v2 0/3] [PATCH v2 0/3] Kernel Userspace Protection for Radix MMU Russell Currey
2018-12-10 7:00 ` [PATCH v2 1/3] powerpc/mm/radix: Use KUEP API " Russell Currey
@ 2018-12-10 7:00 ` Russell Currey
2018-12-17 7:09 ` Christophe Leroy
2018-12-10 7:00 ` [PATCH v2 3/3] powerpc/64s: Implement KUAP for Radix MMU Russell Currey
2 siblings, 1 reply; 7+ messages in thread
From: Russell Currey @ 2018-12-10 7:00 UTC (permalink / raw)
To: linuxppc-dev
Cc: mikey, mpe, benh, npiggin, christophe.leroy, kernel-hardening,
Russell Currey
__patch_instruction() is called in early boot, and uses
__put_user_size(), which includes the locks and unlocks for KUAP,
which could either be called too early, or in the Radix case, forced to
use "early_" versions of functions just to safely handle this one case.
__put_user_asm() does not do this, and thus is safe to use both in early
boot, and later on since in this case it should only ever be touching
kernel memory.
__patch_instruction() was previously refactored to use __put_user_size()
in order to be able to return -EFAULT, which would allow the kernel to
patch instructions in userspace, which should never happen. This has
the functional change of causing faults on userspace addresses if KUAP
is turned on, which should never happen in practice.
A future enhancement could be to double check the patch address is
definitely allowed to be tampered with by the kernel.
Signed-off-by: Russell Currey <ruscur@russell.cc>
---
arch/powerpc/lib/code-patching.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 89502cbccb1b..15e8c6339960 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -26,9 +26,9 @@
static int __patch_instruction(unsigned int *exec_addr, unsigned int instr,
unsigned int *patch_addr)
{
- int err;
+ int err = 0;
- __put_user_size(instr, patch_addr, 4, err);
+ __put_user_asm(instr, patch_addr, err, "stw");
if (err)
return err;
--
2.19.2
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v2 3/3] powerpc/64s: Implement KUAP for Radix MMU
2018-12-10 7:00 [PATCH v2 0/3] [PATCH v2 0/3] Kernel Userspace Protection for Radix MMU Russell Currey
2018-12-10 7:00 ` [PATCH v2 1/3] powerpc/mm/radix: Use KUEP API " Russell Currey
2018-12-10 7:00 ` [PATCH v2 2/3] powerpc/lib: Refactor __patch_instruction() to use __put_user_asm() Russell Currey
@ 2018-12-10 7:00 ` Russell Currey
2 siblings, 0 replies; 7+ messages in thread
From: Russell Currey @ 2018-12-10 7:00 UTC (permalink / raw)
To: linuxppc-dev
Cc: mikey, mpe, benh, npiggin, christophe.leroy, kernel-hardening,
Russell Currey
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:
- exiting the kernel and entering userspace
- performing an operation like copy_{to/from}_user()
- context switching to a process that has access enabled
and similarly, access is disabled again when exiting userspace and
entering the kernel.
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.
The KUAP state is tracked in the PACA because reading the register
that manages these accesses is costly. This Has the unfortunate
downside of another layer of abstraction for platforms that implement
the locks and unlocks, but this could be useful in future for other
things too, like counters for benchmarking or smartly handling lots
of small accesses at once.
Signed-off-by: Russell Currey <ruscur@russell.cc>
---
.../powerpc/include/asm/book3s/64/kup-radix.h | 36 +++++++++++++++++++
arch/powerpc/include/asm/exception-64s.h | 15 ++++++--
arch/powerpc/include/asm/kup.h | 3 ++
arch/powerpc/include/asm/mmu.h | 9 ++++-
arch/powerpc/include/asm/reg.h | 1 +
arch/powerpc/mm/pgtable-radix.c | 14 ++++++++
arch/powerpc/mm/pkeys.c | 7 ++--
arch/powerpc/platforms/Kconfig.cputype | 1 +
8 files changed, 81 insertions(+), 5 deletions(-)
create mode 100644 arch/powerpc/include/asm/book3s/64/kup-radix.h
diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h b/arch/powerpc/include/asm/book3s/64/kup-radix.h
new file mode 100644
index 000000000000..93273ca99310
--- /dev/null
+++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_KUP_RADIX_H
+#define _ASM_POWERPC_KUP_RADIX_H
+
+#ifndef __ASSEMBLY__
+#ifdef CONFIG_PPC_KUAP
+#include <asm/reg.h>
+/*
+ * We do have the ability to individually lock/unlock reads and writes rather
+ * than both at once, however it's a significant performance hit due to needing
+ * to do a read-modify-write, which adds a mfspr, which is slow. As a result,
+ * locking/unlocking both at once is preferred.
+ */
+static inline void unlock_user_access(void __user *to, const void __user *from,
+ unsigned long size)
+{
+ if (!mmu_has_feature(MMU_FTR_RADIX_KUAP))
+ return;
+
+ mtspr(SPRN_AMR, 0);
+ isync();
+ get_paca()->user_access_allowed = 1;
+}
+
+static inline void lock_user_access(void __user *to, const void __user *from,
+ unsigned long size)
+{
+ if (!mmu_has_feature(MMU_FTR_RADIX_KUAP))
+ return;
+
+ mtspr(SPRN_AMR, AMR_LOCKED);
+ get_paca()->user_access_allowed = 0;
+}
+#endif /* CONFIG_PPC_KUAP */
+#endif /* __ASSEMBLY__ */
+#endif
diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 4d971ca1e69b..0ed4923c1282 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -264,8 +264,19 @@ BEGIN_FTR_SECTION_NESTED(943) \
std ra,offset(r13); \
END_FTR_SECTION_NESTED(ftr,ftr,943)
-#define LOCK_USER_ACCESS(reg)
-#define UNLOCK_USER_ACCESS(reg)
+#define LOCK_USER_ACCESS(reg) \
+BEGIN_MMU_FTR_SECTION_NESTED(944) \
+ lis reg,(AMR_LOCKED)@highest; \
+ rldicr reg,reg,32,31; \
+ mtspr SPRN_AMR,reg; \
+END_MMU_FTR_SECTION_NESTED(MMU_FTR_RADIX_KUAP,MMU_FTR_RADIX_KUAP,944)
+
+#define UNLOCK_USER_ACCESS(reg) \
+BEGIN_MMU_FTR_SECTION_NESTED(945) \
+ li reg,0; \
+ mtspr SPRN_AMR,reg; \
+ isync; \
+END_MMU_FTR_SECTION_NESTED(MMU_FTR_RADIX_KUAP,MMU_FTR_RADIX_KUAP,945)
#define EXCEPTION_PROLOG_0(area) \
GET_PACA(r13); \
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 16ff3f9da29c..7813e2bcfb7c 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -8,6 +8,9 @@
#ifdef CONFIG_PPC_BOOK3S_32
#include <asm/book3s/32/kup.h>
#endif
+#ifdef CONFIG_PPC_BOOK3S_64
+#include <asm/book3s/64/kup-radix.h>
+#endif
#ifndef __ASSEMBLY__
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index eb20eb3b8fb0..048df188fc10 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -107,6 +107,10 @@
*/
#define MMU_FTR_1T_SEGMENT ASM_CONST(0x40000000)
+/* Supports KUAP (key 0 controlling userspace addresses) on radix
+ */
+#define MMU_FTR_RADIX_KUAP ASM_CONST(0x80000000)
+
/* MMU feature bit sets for various CPUs */
#define MMU_FTRS_DEFAULT_HPTE_ARCH_V2 \
MMU_FTR_HPTE_TABLE | MMU_FTR_PPCAS_ARCH_V2
@@ -143,7 +147,10 @@ enum {
MMU_FTR_KERNEL_RO | MMU_FTR_68_BIT_VA |
#ifdef CONFIG_PPC_RADIX_MMU
MMU_FTR_TYPE_RADIX |
-#endif
+#ifdef CONFIG_PPC_KUAP
+ MMU_FTR_RADIX_KUAP |
+#endif /* CONFIG_PPC_KUAP */
+#endif /* CONFIG_PPC_RADIX_MMU */
0,
};
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index c9c382e57017..6b5d2a61af5a 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -246,6 +246,7 @@
#define SPRN_DSCR 0x11
#define SPRN_CFAR 0x1c /* Come From Address Register */
#define SPRN_AMR 0x1d /* Authority Mask Register */
+#define AMR_LOCKED 0xC000000000000000UL /* Read & Write disabled */
#define SPRN_UAMOR 0x9d /* User Authority Mask Override Register */
#define SPRN_AMOR 0x15d /* Authority Mask Override Register */
#define SPRN_ACOP 0x1F /* Available Coprocessor Register */
diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index 3565e266994b..e248f330d6fd 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -29,6 +29,7 @@
#include <asm/powernv.h>
#include <asm/sections.h>
#include <asm/trace.h>
+#include <asm/uaccess.h>
#include <trace/events/thp.h>
@@ -552,6 +553,19 @@ void __init setup_kuep(bool disabled)
}
#endif
+#ifdef CONFIG_PPC_KUAP
+void __init setup_kuap(bool disabled)
+{
+ if (disabled || !early_radix_enabled())
+ return;
+
+ pr_info("Activating Kernel Userspace Access Prevention\n");
+
+ cur_cpu_spec->mmu_features |= MMU_FTR_RADIX_KUAP;
+ mtspr(SPRN_AMR, AMR_LOCKED);
+}
+#endif
+
void __init radix__early_init_mmu(void)
{
unsigned long lpcr;
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index b271b283c785..bb3cf915016f 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -7,6 +7,7 @@
#include <asm/mman.h>
#include <asm/setup.h>
+#include <asm/uaccess.h>
#include <linux/pkeys.h>
#include <linux/of_device.h>
@@ -266,7 +267,8 @@ int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
void thread_pkey_regs_save(struct thread_struct *thread)
{
- if (static_branch_likely(&pkey_disabled))
+ if (static_branch_likely(&pkey_disabled) &&
+ !mmu_has_feature(MMU_FTR_RADIX_KUAP))
return;
/*
@@ -280,7 +282,8 @@ void thread_pkey_regs_save(struct thread_struct *thread)
void thread_pkey_regs_restore(struct thread_struct *new_thread,
struct thread_struct *old_thread)
{
- if (static_branch_likely(&pkey_disabled))
+ if (static_branch_likely(&pkey_disabled) &&
+ !mmu_has_feature(MMU_FTR_RADIX_KUAP))
return;
if (old_thread->amr != new_thread->amr)
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 48cc8df0fdd2..0b9a8eda413a 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -336,6 +336,7 @@ config PPC_RADIX_MMU
depends on PPC_BOOK3S_64
select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
select PPC_HAVE_KUEP
+ select PPC_HAVE_KUAP
default y
help
Enable support for the Power ISA 3.0 Radix style MMU. Currently this
--
2.19.2
^ permalink raw reply related [flat|nested] 7+ messages in thread