arm64: kernel: Don't toggle PAN on systems with UAO
If a CPU supports both Privileged Access Never (PAN) and User Access
Override (UAO), we don't need to disable/re-enable PAN round all
copy_to_user() like calls.
UAO alternatives cause these calls to use the 'unprivileged' load/store
instructions, which are overridden to be the privileged kind when
fs==KERNEL_DS.
This patch changes the copy_to_user() calls to have their PAN toggling
depend on a new composite 'feature' ARM64_ALT_PAN_NOT_UAO.
If both features are detected, PAN will be enabled, but the copy_to_user()
alternatives will not be applied. This means PAN will be enabled all the
time for these functions. If only PAN is detected, the toggling will be
enabled as normal.
This will save the time taken to disable/re-enable PAN, and allow us to
catch copy_to_user() accesses that occur with fs==KERNEL_DS.
Futex and swp-emulation code continue to hang their PAN toggling code on
ARM64_HAS_PAN.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index a5df7cd..37a53fc 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -32,8 +32,9 @@
#define ARM64_WORKAROUND_834220 7
#define ARM64_HAS_NO_HW_PREFETCH 8
#define ARM64_HAS_UAO 9
+#define ARM64_ALT_PAN_NOT_UAO 10
-#define ARM64_NCAPS 10
+#define ARM64_NCAPS 11
#ifndef __ASSEMBLY__
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index f973bdc..16ba0d5 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -145,7 +145,7 @@
do { \
unsigned long __gu_val; \
__chk_user_ptr(ptr); \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN, \
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_ALT_PAN_NOT_UAO,\
CONFIG_ARM64_PAN)); \
switch (sizeof(*(ptr))) { \
case 1: \
@@ -168,7 +168,7 @@
BUILD_BUG(); \
} \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN, \
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_ALT_PAN_NOT_UAO,\
CONFIG_ARM64_PAN)); \
} while (0)
@@ -217,7 +217,7 @@
do { \
__typeof__(*(ptr)) __pu_val = (x); \
__chk_user_ptr(ptr); \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN, \
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_ALT_PAN_NOT_UAO,\
CONFIG_ARM64_PAN)); \
switch (sizeof(*(ptr))) { \
case 1: \
@@ -239,7 +239,7 @@
default: \
BUILD_BUG(); \
} \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN, \
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_ALT_PAN_NOT_UAO,\
CONFIG_ARM64_PAN)); \
} while (0)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9cc8186..7566cad 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -67,6 +67,10 @@
.width = 0, \
}
+/* meta feature for alternatives */
+static bool __maybe_unused
+cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry);
+
static struct arm64_ftr_bits ftr_id_aa64isar0[] = {
ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
@@ -688,6 +692,12 @@
.enable = cpu_enable_uao,
},
#endif /* CONFIG_ARM64_UAO */
+#ifdef CONFIG_ARM64_PAN
+ {
+ .capability = ARM64_ALT_PAN_NOT_UAO,
+ .matches = cpufeature_pan_not_uao,
+ },
+#endif /* CONFIG_ARM64_PAN */
{},
};
@@ -966,3 +976,9 @@
pr_warn("L1_CACHE_BYTES smaller than the Cache Writeback Granule (%d < %d)\n",
L1_CACHE_BYTES, cls);
}
+
+static bool __maybe_unused
+cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry)
+{
+ return (cpus_have_cap(ARM64_HAS_PAN) && !cpus_have_cap(ARM64_HAS_UAO));
+}
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index 3f950b6..5d1cad3 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -33,7 +33,7 @@
* Alignment fixed up by hardware.
*/
ENTRY(__clear_user)
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
mov x2, x1 // save the size for fixup return
subs x1, x1, #8
@@ -54,7 +54,7 @@
b.mi 5f
uao_user_alternative 9f, strb, sttrb, wzr, x0, 0
5: mov x0, #0
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
ret
ENDPROC(__clear_user)
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 1d982d6..17e8306 100644
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -67,11 +67,11 @@
end .req x5
ENTRY(__copy_from_user)
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
add end, x0, x2
#include "copy_template.S"
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
mov x0, #0 // Nothing to copy
ret
diff --git a/arch/arm64/lib/copy_in_user.S b/arch/arm64/lib/copy_in_user.S
index feaad15..f7292dd0 100644
--- a/arch/arm64/lib/copy_in_user.S
+++ b/arch/arm64/lib/copy_in_user.S
@@ -68,11 +68,11 @@
end .req x5
ENTRY(__copy_in_user)
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
add end, x0, x2
#include "copy_template.S"
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
mov x0, #0
ret
diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 2dae2cd..21faae6 100644
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S
@@ -66,11 +66,11 @@
end .req x5
ENTRY(__copy_to_user)
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
add end, x0, x2
#include "copy_template.S"
-ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_HAS_PAN, \
+ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
mov x0, #0
ret
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 820d473..d0762a7 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -234,6 +234,9 @@
}
if (permission_fault(esr) && (addr < USER_DS)) {
+ if (get_thread_info(regs->sp)->addr_limit == KERNEL_DS)
+ panic("Accessing user space memory with fs=KERNEL_DS");
+
if (!search_exception_tables(regs->pc))
panic("Accessing user space memory outside uaccess.h routines");
}