linux-hardening - [RESEND PATCH v4 01/11] powerpc: Add LKDTM accessor for patching addr

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Message-Id: <20210506043452.9674-2-cmr@linux.ibm.com>
Date:   Wed,  5 May 2021 23:34:42 -0500
From:   "Christopher M. Riedl" <cmr@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     tglx@...utronix.de, x86@...nel.org,
        linux-hardening@...r.kernel.org, keescook@...omium.org
Subject: [RESEND PATCH v4 01/11] powerpc: Add LKDTM accessor for patching addr

When live patching with STRICT_KERNEL_RWX a mapping is installed at a
"patching address" with temporary write permissions. Provide a
LKDTM-only accessor function for this address in preparation for a LKDTM
test which attempts to "hijack" this mapping by writing to it from
another CPU.

Signed-off-by: Christopher M. Riedl <cmr@...ux.ibm.com>
---
 arch/powerpc/include/asm/code-patching.h | 4 ++++
 arch/powerpc/lib/code-patching.c         | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index f1d029bf906e5..e51c81e4a9bda 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -188,4 +188,8 @@ static inline unsigned long ppc_kallsyms_lookup_name(const char *name)
 				 ___PPC_RA(__REG_R1) | PPC_LR_STKOFF)
 #endif /* CONFIG_PPC64 */
 
+#if IS_BUILTIN(CONFIG_LKDTM) && IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)
+unsigned long read_cpu_patching_addr(unsigned int cpu);
+#endif
+
 #endif /* _ASM_POWERPC_CODE_PATCHING_H */
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 870b30d9be2f8..2b1b3e9043ade 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -48,6 +48,13 @@ int raw_patch_instruction(struct ppc_inst *addr, struct ppc_inst instr)
 #ifdef CONFIG_STRICT_KERNEL_RWX
 static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
 
+#if IS_BUILTIN(CONFIG_LKDTM)
+unsigned long read_cpu_patching_addr(unsigned int cpu)
+{
+	return (unsigned long)(per_cpu(text_poke_area, cpu))->addr;
+}
+#endif
+
 static int text_area_cpu_up(unsigned int cpu)
 {
 	struct vm_struct *area;
-- 
2.26.1