[PATCH v2 1/2] arm64/crash_core: Export KERNELPACMASK in vmcoreinfo

[Amit Daniel Kachhap]

Recently arm64 linux kernel added support for Armv8.3-A Pointer
Authentication feature. If this feature is enabled in the kernel and the
hardware supports address authentication then the return addresses are
signed and stored in the stack to prevent ROP kind of attack. Kdump tool
will now dump the kernel with signed lr values in the stack.

Any user analysis tool for this kernel dump may need the kernel pac mask
information in vmcoreinfo to generate the correct return address for
stacktrace purpose as well as to resolve the symbol name.

This patch is similar to commit ec6e822d1a22d0eef ("arm64: expose user PAC
bit positions via ptrace") which exposes pac mask information via ptrace
interfaces.

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
---
Changes since v1:
* Rebased to kernel 5.7-rc3.
* commit log change.

An implementation of this new KERNELPACMASK vmcoreinfo field used by crash
tool can be found here[1]. This change is accepted by crash utility
maintainer [2].

[1]: https://www.redhat.com/archives/crash-utility/2020-April/msg00095.html
[2]: https://www.redhat.com/archives/crash-utility/2020-April/msg00099.html

 arch/arm64/include/asm/compiler.h | 3 +++
 arch/arm64/kernel/crash_core.c    | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h
index eece20d..32d5900 100644
--- a/arch/arm64/include/asm/compiler.h
+++ b/arch/arm64/include/asm/compiler.h
@@ -19,6 +19,9 @@
 #define __builtin_return_address(val)					\
 	(void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val)))
 
+#else  /* !CONFIG_ARM64_PTR_AUTH */
+#define	ptrauth_user_pac_mask()		0ULL
+#define	ptrauth_kernel_pac_mask()	0ULL
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
 #endif /* __ASM_COMPILER_H */
diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c
index ca4c3e1..25cf2ce 100644
--- a/arch/arm64/kernel/crash_core.c
+++ b/arch/arm64/kernel/crash_core.c
@@ -6,6 +6,7 @@
 
 #include <linux/crash_core.h>
 #include <asm/memory.h>
+#include <asm/pointer_auth.h>
 
 void arch_crash_save_vmcoreinfo(void)
 {
@@ -16,4 +17,7 @@ void arch_crash_save_vmcoreinfo(void)
 	vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n",
 						PHYS_OFFSET);
 	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
+	vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n",
+						system_supports_address_auth() ?
+						ptrauth_kernel_pac_mask() : 0);
 }
-- 
2.7.4