[PATCH v8 4/6] arm64: cpufeature: Modify address authentication cpufeature to exact

Amit Daniel Kachhap
2020-09-14T08:38:51Z

The current address authentication cpufeature levels are set as LOWER_SAFE
which is not compatible with the different configurations added for Armv8.3
ptrauth enhancements as the different levels have different behaviour and
there is no tunable to enable the lower safe versions. This is rectified
by setting those cpufeature type as EXACT.

The current cpufeature framework also does not interfere in the booting of
non-exact secondary cpus but rather marks them as tainted. As a workaround
this is fixed by replacing the generic match handler with a new handler
specific to ptrauth.

After this change, if there is any variation in ptrauth configurations in
secondary cpus from boot cpu then those mismatched cpus are parked in an
infinite loop.

Following ptrauth crash log is observed in Arm fastmodel with simulated
mismatched cpus without this fix,

CPU features: SANITY CHECK: Unexpected variation in SYS_ID_AA64ISAR1_EL1. Boot CPU: 0x11111110211402, CPU4: 0x11111110211102
CPU features: Unsupported CPU feature variation detected.
GICv3: CPU4: found redistributor 100 region 0:0x000000002f180000
CPU4: Booted secondary processor 0x0000000100 [0x410fd0f0]
Unable to handle kernel paging request at virtual address bfff800010dadf3c
Mem abort info:
ESR = 0x86000004
EC = 0x21: IABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
[bfff800010dadf3c] address between user and kernel address ranges
Internal error: Oops: 86000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 4 PID: 29 Comm: migration/4 Tainted: G S 5.8.0-rc4-00005-ge658591d66d1-dirty #158
Hardware name: Foundation-v8A (DT)
pstate: 60000089 (nZCv daIf -PAN -UAO BTYPE=--)
pc : 0xbfff800010dadf3c
lr : __schedule+0x2b4/0x5a8
sp : ffff800012043d70
x29: ffff800012043d70 x28: 0080000000000000
x27: ffff800011cbe000 x26: ffff00087ad37580
x25: ffff00087ad37000 x24: ffff800010de7d50
x23: ffff800011674018 x22: 0784800010dae2a8
x21: ffff00087ad37000 x20: ffff00087acb8000
x19: ffff00087f742100 x18: 0000000000000030
x17: 0000000000000000 x16: 0000000000000000
x15: ffff800011ac1000 x14: 00000000000001bd
x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 71519a147ddfeb82
x9 : 825d5ec0fb246314 x8 : ffff00087ad37dd8
x7 : 0000000000000000 x6 : 00000000fffedb0e
x5 : 00000000ffffffff x4 : 0000000000000000
x3 : 0000000000000028 x2 : ffff80086e11e000
x1 : ffff00087ad37000 x0 : ffff00087acdc600
Call trace:
0xbfff800010dadf3c
schedule+0x78/0x110
schedule_preempt_disabled+0x24/0x40
__kthread_parkme+0x68/0xd0
kthread+0x138/0x160
ret_from_fork+0x10/0x34
Code: bad PC value

After this fix, the mismatched CPU4 is parked as,
CPU features: CPU4: Detected conflict for capability 39 (Address authentication (IMP DEF algorithm)), System: 1, CPU: 0
CPU4: will not boot
CPU4: failed to come online
CPU4: died during early boot

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
[Suzuki: Introduce new matching function for address authentication]
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
Changes since v7:
* Removed extra checks for secondary CPUs.
* Updated the commit logs to represent the behaviour before/after this fix.

arch/arm64/kernel/cpufeature.c | 44 +++++++++++++++++++++++++++-------
1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6424584be01e..fdbc26c0d712 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -197,9 +197,9 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = {
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_FCMA_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_JSCVT_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
- FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_API_SHIFT, 4, 0),
+ FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_API_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
- FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_APA_SHIFT, 4, 0),
+ FTR_STRICT, FTR_EXACT, ID_AA64ISAR1_APA_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR1_DPB_SHIFT, 4, 0),
ARM64_FTR_END,
};
@@ -1648,11 +1648,37 @@ static void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused)
#endif /* CONFIG_ARM64_RAS_EXTN */

#ifdef CONFIG_ARM64_PTR_AUTH
-static bool has_address_auth(const struct arm64_cpu_capabilities *entry,
- int __unused)
+static bool has_address_auth_cpucap(const struct arm64_cpu_capabilities *entry, int scope)
{
- return __system_matches_cap(ARM64_HAS_ADDRESS_AUTH_ARCH) ||
- __system_matches_cap(ARM64_HAS_ADDRESS_AUTH_IMP_DEF);
+ int boot_val, sec_val;
+
+ /* We don't expect to be called with SCOPE_SYSTEM */
+ WARN_ON(scope == SCOPE_SYSTEM);
+ /*
+ * The ptr-auth feature levels are not intercompatible with lower
+ * levels. Hence we must match ptr-auth feature level of the secondary
+ * CPUs with that of the boot CPU. The level of boot cpu is fetched
+ * from the sanitised register whereas direct register read is done for
+ * the secondary CPUs.
+ * The sanitised feature state is guaranteed to match that of the
+ * boot CPU as a mismatched secondary CPU is parked before it gets
+ * a chance to update the state, with the capability.
+ */
+ boot_val = cpuid_feature_extract_field(read_sanitised_ftr_reg(entry->sys_reg),
+ entry->field_pos, entry->sign);
+ if (scope & SCOPE_BOOT_CPU)
+ return boot_val >= entry->min_field_value;
+ /* Now check for the secondary CPUs with SCOPE_LOCAL_CPU scope */
+ sec_val = cpuid_feature_extract_field(__read_sysreg_by_encoding(entry->sys_reg),
+ entry->field_pos, entry->sign);
+ return sec_val == boot_val;
+}
+
+static bool has_address_auth_metacap(const struct arm64_cpu_capabilities *entry,
+ int scope)
+{
+ return has_address_auth_cpucap(cpu_hwcaps_ptrs[ARM64_HAS_ADDRESS_AUTH_ARCH], scope) ||
+ has_address_auth_cpucap(cpu_hwcaps_ptrs[ARM64_HAS_ADDRESS_AUTH_IMP_DEF], scope);
}

static bool has_generic_auth(const struct arm64_cpu_capabilities *entry,
@@ -2021,7 +2047,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.sign = FTR_UNSIGNED,
.field_pos = ID_AA64ISAR1_APA_SHIFT,
.min_field_value = ID_AA64ISAR1_APA_ARCHITECTED,
- .matches = has_cpuid_feature,
+ .matches = has_address_auth_cpucap,
},
{
.desc = "Address authentication (IMP DEF algorithm)",
@@ -2031,12 +2057,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.sign = FTR_UNSIGNED,
.field_pos = ID_AA64ISAR1_API_SHIFT,
.min_field_value = ID_AA64ISAR1_API_IMP_DEF,
- .matches = has_cpuid_feature,
+ .matches = has_address_auth_cpucap,
},
{
.capability = ARM64_HAS_ADDRESS_AUTH,
.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
- .matches = has_address_auth,
+ .matches = has_address_auth_metacap,
},
{
.desc = "Generic authentication (architected algorithm)",