On arm64 the TCR_EL1.TBI0 bit has been set since Linux 3.x hence
the userspace (EL0) is allowed to set a non-zero value in the top
byte but the resulting pointers are not allowed at the user-kernel
syscall ABI boundary.
This patch sets ARM64_AT_FLAGS_SYSCALL_TBI (bit[0]) in the AT_FLAGS
to advertise the relaxation of the ABI to the userspace.
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
CC: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
---
arch/arm64/include/asm/atflags.h | 7 +++++++
arch/arm64/include/asm/elf.h | 5 +++++
arch/arm64/include/uapi/asm/atflags.h | 8 ++++++++
3 files changed, 20 insertions(+)
create mode 100644 arch/arm64/include/asm/atflags.h
create mode 100644 arch/arm64/include/uapi/asm/atflags.h
diff --git a/arch/arm64/include/asm/atflags.h b/arch/arm64/include/asm/atflags.h
new file mode 100644
index 000000000000..b20093d61bf2
--- /dev/null
+++ b/arch/arm64/include/asm/atflags.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_ATFLAGS_H
+#define __ASM_ATFLAGS_H
+
+#include <uapi/asm/atflags.h>
+
+#endif
diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 433b9554c6a1..da5a6d310ff4 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -16,6 +16,7 @@
#ifndef __ASM_ELF_H
#define __ASM_ELF_H
+#include <asm/atflags.h>
#include <asm/hwcap.h>
/*
@@ -163,6 +164,10 @@ do { \
NEW_AUX_ENT(AT_IGNORE, 0); \
} while (0)
+/* Platform specific AT_FLAGS */
+#define ELF_AT_FLAGS ARM64_AT_FLAGS_SYSCALL_TBI
+#define COMPAT_ELF_AT_FLAGS 0
+
#define ARCH_HAS_SETUP_ADDITIONAL_PAGES
struct linux_binprm;
extern int arch_setup_additional_pages(struct linux_binprm *bprm,
diff --git a/arch/arm64/include/uapi/asm/atflags.h b/arch/arm64/include/uapi/asm/atflags.h
new file mode 100644
index 000000000000..1cf25692ffd6
--- /dev/null
+++ b/arch/arm64/include/uapi/asm/atflags.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UAPI_ASM_ATFLAGS_H
+#define __UAPI_ASM_ATFLAGS_H
+
+/* Platform specific AT_FLAGS */
+#define ARM64_AT_FLAGS_SYSCALL_TBI (1 << 0)
+
+#endif
--
2.19.2
