Commit 60d043c1 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
Browse files

arm64: Avoid #define'ing PTE_MAYBE_NG to 0x0 for asm use 



The PROT_* macros resolve to expressions that are only valid in C and
not in assembler, and so they are only usable from C code. Currently, we
make an exception for the permission indirection init code in proc.S,
which doesn't care about the bits that are conditionally set, and so we
just #define PTE_MAYBE_NG to 0x0 for any assembler file that includes
these definitions.

This is dodgy because this means that PROT_NORMAL and friends is
generally available in asm code, but defined in a way that deviates from
the definition that C code will observe, which might lead to hard to
diagnose issues down the road.

So instead, #define PTE_MAYBE_NG only in the place where the PIE
constants are evaluated, and #undef it again right after. This allows us
to drop the #define from pgtable-prot.h, and avoid the risk of deviating
definitions between asm and C.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-72-ardb+git@google.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 68aec33f

arch/arm64/include/asm/pgtable-prot.h

+0 −4
Original line number Diff line number Diff line
@@ -57,10 +57,6 @@ 
#define _PAGE_READONLY_EXEC	(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN)

#define _PAGE_EXECONLY		(_PAGE_DEFAULT | PTE_RDONLY | PTE_NG | PTE_PXN)



#ifdef __ASSEMBLY__

#define PTE_MAYBE_NG	0

#endif



#ifndef __ASSEMBLY__



#include <asm/cpufeature.h>

arch/arm64/mm/proc.S

+13 −0
Original line number Diff line number Diff line
@@ -456,11 +456,24 @@ alternative_else_nop_endif 
	ubfx	x1, x1, #ID_AA64MMFR3_EL1_S1PIE_SHIFT, #4

	cbz	x1, .Lskip_indirection



	/*

	 * The PROT_* macros describing the various memory types may resolve to

	 * C expressions if they include the PTE_MAYBE_* macros, and so they

	 * can only be used from C code. The PIE_E* constants below are also

	 * defined in terms of those macros, but will mask out those

	 * PTE_MAYBE_* constants, whether they are set or not. So #define them

	 * as 0x0 here so we can evaluate the PIE_E* constants in asm context.

	 */



#define PTE_MAYBE_NG		0



	mov_q	x0, PIE_E0

	msr	REG_PIRE0_EL1, x0

	mov_q	x0, PIE_E1

	msr	REG_PIR_EL1, x0



#undef PTE_MAYBE_NG



	mov	x0, TCR2_EL1x_PIE

	msr	REG_TCR2_EL1, x0