[RFT PATCH v2 13/23] x86/linkage: Add SYM_PIC_ALIAS() macro helper to emit symbol aliases

Ard Biesheuvel
2025-05-04T09:53:33Z

From: Ard Biesheuvel <ardb@kernel.org>

Startup code that may execute from the early 1:1 mapping of memory will
be confined into its own address space, and only be permitted to access
ordinary kernel symbols if this is known to be safe.

Introduce a macro helper SYM_PIC_ALIAS() that emits a __pi_ prefixed
alias for a symbol, which allows startup code to access it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/include/asm/linkage.h | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index b51d8a4673f5..9d38ae744a2e 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -141,5 +141,15 @@
#define SYM_FUNC_START_WEAK_NOALIGN(name) \
SYM_START(name, SYM_L_WEAK, SYM_A_NONE)

+/*
+ * Expose 'sym' to the startup code in arch/x86/boot/startup/, by emitting an
+ * alias prefixed with __pi_
+ */
+#ifdef __ASSEMBLER__
+#define SYM_PIC_ALIAS(sym) SYM_ALIAS(__pi_ ## sym, sym, SYM_L_GLOBAL)
+#else
+#define SYM_PIC_ALIAS(sym) extern typeof(sym) __PASTE(__pi_, sym) __alias(sym)
+#endif
+
#endif /* _ASM_X86_LINKAGE_H */

--
2.49.0.906.g1f30a19c02-goog