[PATCH v3 0/2] arm64: introduce run-time detection of aarch32 support

[PATCH v3 0/2] arm64: introduce run-time detection of aarch32 support

[Yury Norov]

This is needed to avoid loading aarch32 binaries if COMPAT is enabled, but
aarch32 is not supported by specific platform.

First patch fixes hidden header dependencies in arch/arm64/include/asm/cpufeature.h.
It's not related to the issue, but helps to avoid build failure that happens
if one applies second patch only.

Second patch adds run-time detection of aarch32 support, and rejects kernel to
load such binaries, if not supported.

Tested on ThunderX.

V3:
 - first patch message extended with explanation for cpu_feature macro move;
 - in second patch, restored pfr0 masking in id_aa64pfr0_aarch32_el0().

V2:
 - add missing <linux/compiler.h> for the __attribute_const__ on
   cpuid_feature_extract_field;
 - move cpu_feature macro under the __ASSEMBLY__ guard.
 - check that all CPUs support AArch32, not the current only,
   the same way as for endianness support.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>

Yury Norov (2):
  arm64: cpufeature.h: resolve hidden header dependencies
  arm64: don't load 32-bit binaries if platform has no aarch32_el0

 arch/arm64/include/asm/cpufeature.h | 10 +++++++++-
 arch/arm64/include/asm/cputype.h    |  8 ++++++++
 arch/arm64/include/asm/elf.h        |  6 ++++--
 arch/arm64/kernel/cpuinfo.c         | 12 ++++++++++++
 4 files changed, 33 insertions(+), 3 deletions(-)

-- 
2.1.4

[PATCH v3 1/2] arm64: cpufeature.h: resolve hidden header dependencies

[Yury Norov]

Functions implemented in cpufeature.h depend on some headers, but
cpufeature.h does not include them. This may cause build failure if
cpufeature.h user does not include that headers by itself. (Like it
happens in next patch of this series.)

cpu_feature macro is moved under "#ifndef __ASSEMBLY__" guard as
it depends on <linux/log2.h>, and can be used in C files only.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c104421..f0e4017 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -19,7 +19,6 @@
  */
 
 #define MAX_CPU_FEATURES	(8 * sizeof(elf_hwcap))
-#define cpu_feature(x)		ilog2(HWCAP_ ## x)
 
 #define ARM64_WORKAROUND_CLEAN_CACHE		0
 #define ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE	1
@@ -30,6 +29,14 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/bitmap.h>
+#include <linux/compiler.h>
+#include <linux/log2.h>
+#include <linux/printk.h>
+#include <linux/types.h>
+
+#define cpu_feature(x)		ilog2(HWCAP_ ## x)
+
 struct arm64_cpu_capabilities {
 	const char *desc;
 	u16 capability;
-- 
2.1.4

[PATCH v3 2/2] arm64: don't load 32-bit binaries if platform has no aarch32_el0

[Yury Norov]

Kernel option COMPAT defines the ability of executing aarch32 binaries.
Some platforms does not support aarch32 mode, and so cannot execute that
binaries. But we cannot just disable COMPAT for them because the same
kernel binary may be used by multiple platforms.

In this patch, system_supports_aarch32_el0() is introduced to detect
aarch32 support at run-time.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
 arch/arm64/include/asm/cpufeature.h |  1 +
 arch/arm64/include/asm/cputype.h    |  9 +++++++++
 arch/arm64/include/asm/elf.h        |  6 ++++--
 arch/arm64/kernel/cpuinfo.c         | 12 ++++++++++++
 4 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index f0e4017..35f2654 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -83,6 +83,7 @@ void check_local_cpu_errata(void);
 void check_local_cpu_features(void);
 bool cpu_supports_mixed_endian_el0(void);
 bool system_supports_mixed_endian_el0(void);
+bool system_supports_aarch32_el0(void);
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index a84ec60..5fb5585 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -81,6 +81,10 @@
 #define ID_AA64MMFR0_BIGEND(mmfr0)	\
 	(((mmfr0) & ID_AA64MMFR0_BIGEND_MASK) >> ID_AA64MMFR0_BIGEND_SHIFT)
 
+#define ID_AA64PFR0_EL0_64	1
+#define ID_AA64PFR0_EL0_6432	2
+#define ID_AA64PFR0_EL0_MASK	0xf
+
 #define SCTLR_EL1_CP15BEN	(0x1 << 5)
 #define SCTLR_EL1_SED		(0x1 << 8)
 
@@ -116,6 +120,11 @@ static inline u32 __attribute_const__ read_cpuid_cachetype(void)
 	return read_cpuid(CTR_EL0);
 }
 
+static inline bool id_aa64pfr0_aarch32_el0(u64 pfr0)
+{
+	return (pfr0 & ID_AA64PFR0_EL0_MASK) == ID_AA64PFR0_EL0_6432;
+}
+
 static inline bool id_aa64mmfr0_mixed_endian_el0(u64 mmfr0)
 {
 	return (ID_AA64MMFR0_BIGEND(mmfr0) == 0x1) ||
diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index faad6df..461897b 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -21,6 +21,7 @@
 /*
  * ELF register definitions..
  */
+#include <asm/cpufeature.h>
 #include <asm/ptrace.h>
 #include <asm/user.h>
 
@@ -173,8 +174,9 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
 
 /* AArch32 EABI. */
 #define EF_ARM_EABI_MASK		0xff000000
-#define compat_elf_check_arch(x)	(((x)->e_machine == EM_ARM) && \
-					 ((x)->e_flags & EF_ARM_EABI_MASK))
+#define compat_elf_check_arch(x)	(system_supports_aarch32_el0()	\
+					&& ((x)->e_machine == EM_ARM)	\
+					&& ((x)->e_flags & EF_ARM_EABI_MASK))
 
 #define compat_start_thread		compat_start_thread
 #define COMPAT_SET_PERSONALITY(ex)	set_thread_flag(TIF_32BIT);
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 75d5a86..4a6ae31 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -36,6 +36,7 @@
 DEFINE_PER_CPU(struct cpuinfo_arm64, cpu_data);
 static struct cpuinfo_arm64 boot_cpu_data;
 static bool mixed_endian_el0 = true;
+static bool aarch32_el0 = true;
 
 static char *icache_policy_str[] = {
 	[ICACHE_POLICY_RESERVED] = "RESERVED/UNKNOWN",
@@ -79,13 +80,24 @@ bool system_supports_mixed_endian_el0(void)
 	return mixed_endian_el0;
 }
 
+bool system_supports_aarch32_el0(void)
+{
+	return aarch32_el0;
+}
+
 static void update_mixed_endian_el0_support(struct cpuinfo_arm64 *info)
 {
 	mixed_endian_el0 &= id_aa64mmfr0_mixed_endian_el0(info->reg_id_aa64mmfr0);
 }
 
+static void update_aarch32_el0_support(struct cpuinfo_arm64 *info)
+{
+	aarch32_el0 &= id_aa64pfr0_aarch32_el0(info->reg_id_aa64pfr0);
+}
+
 static void update_cpu_features(struct cpuinfo_arm64 *info)
 {
+	update_aarch32_el0_support(info);
 	update_mixed_endian_el0_support(info);
 }
 
-- 
2.1.4

[PATCH v3 2/2] arm64: don't load 32-bit binaries if platform has no aarch32_el0

[Suzuki K. Poulose]

On 02/09/15 16:50, Yury Norov wrote:
> Kernel option COMPAT defines the ability of executing aarch32 binaries.
> Some platforms does not support aarch32 mode, and so cannot execute that
> binaries. But we cannot just disable COMPAT for them because the same
> kernel binary may be used by multiple platforms.
>
> In this patch, system_supports_aarch32_el0() is introduced to detect
> aarch32 support at run-time.
>

As such the patch looks good. With my CPU Feature export API patch series,
this will be much more simpler, as we have an API to read the system wide safe
value of pfr0(in this case). I will post the next version of my series
after the merge window.


> Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
> ---
>   arch/arm64/include/asm/cpufeature.h |  1 +
>   arch/arm64/include/asm/cputype.h    |  9 +++++++++
>   arch/arm64/include/asm/elf.h        |  6 ++++--
>   arch/arm64/kernel/cpuinfo.c         | 12 ++++++++++++
>   4 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index f0e4017..35f2654 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -83,6 +83,7 @@ void check_local_cpu_errata(void);
>   void check_local_cpu_features(void);
>   bool cpu_supports_mixed_endian_el0(void);
>   bool system_supports_mixed_endian_el0(void);
> +bool system_supports_aarch32_el0(void);
>
>   #endif /* __ASSEMBLY__ */
>
> diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
> index a84ec60..5fb5585 100644
> --- a/arch/arm64/include/asm/cputype.h
> +++ b/arch/arm64/include/asm/cputype.h
> @@ -81,6 +81,10 @@
>   #define ID_AA64MMFR0_BIGEND(mmfr0)	\
>   	(((mmfr0) & ID_AA64MMFR0_BIGEND_MASK) >> ID_AA64MMFR0_BIGEND_SHIFT)
>
> +#define ID_AA64PFR0_EL0_64	1
> +#define ID_AA64PFR0_EL0_6432	2
> +#define ID_AA64PFR0_EL0_MASK	0xf
> +
>   #define SCTLR_EL1_CP15BEN	(0x1 << 5)
>   #define SCTLR_EL1_SED		(0x1 << 8)
>
> @@ -116,6 +120,11 @@ static inline u32 __attribute_const__ read_cpuid_cachetype(void)
>   	return read_cpuid(CTR_EL0);
>   }
>
> +static inline bool id_aa64pfr0_aarch32_el0(u64 pfr0)
> +{
> +	return (pfr0 & ID_AA64PFR0_EL0_MASK) == ID_AA64PFR0_EL0_6432;

Or you could use (with aarch64 for-next/core branch) :

	return (cpuid_feature_extract_field(pfr0, 0) == ID_AA64PFR0_EL0_6432);


Thanks
Suzuki