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

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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: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-72-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel 2024-02-14 13:29:13 +01:00 committed by Catalin Marinas
parent 68aec33f8f
commit 60d043c101
2 changed files with 13 additions and 4 deletions
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4
arch/arm64/include/asm/pgtable-prot.h
View File

@ -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>

13
arch/arm64/mm/proc.S
View File

@ -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