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[v3,2/6] x86: Add LKDTM accessor for patching addr

Message ID 20200827052659.24922-3-cmr@codefail.de
State New, archived
Headers show
Series Use per-CPU temporary mappings for patching | expand

Commit Message

Christopher M. Riedl Aug. 27, 2020, 5:26 a.m. UTC
When live patching a STRICT_RWX kernel, 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@codefail.de>
 arch/x86/include/asm/text-patching.h | 4 ++++
 arch/x86/kernel/alternative.c        | 7 +++++++
 2 files changed, 11 insertions(+)
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diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index 6593b42cb379..f67b4dd30bf8 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -148,4 +148,8 @@  void int3_emulate_call(struct pt_regs *regs, unsigned long func)
 #endif /* !CONFIG_UML_X86 */
+unsigned long read_cpu_patching_addr(unsigned int cpu);
 #endif /* _ASM_X86_TEXT_PATCHING_H */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c3daf0aaa0ee..c16833f35a1f 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -843,6 +843,13 @@  static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
 __ro_after_init struct mm_struct *poking_mm;
 __ro_after_init unsigned long poking_addr;
+unsigned long read_cpu_patching_addr(unsigned int cpu)
+	return poking_addr;
 static void *__text_poke(void *addr, const void *opcode, size_t len)
 	bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;