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Date: Mon, 24 Jan 2022 18:47:24 +0100 From: Ard Biesheuvel <ardb@...nel.org> To: linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org Cc: linux-hardening@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>, Nicolas Pitre <nico@...xnic.net>, Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>, Keith Packard <keithpac@...zon.com>, Linus Walleij <linus.walleij@...aro.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Tony Lindgren <tony@...mide.com>, Marc Zyngier <maz@...nel.org>, Vladimir Murzin <vladimir.murzin@....com>, Jesse Taube <mr.bossman075@...il.com> Subject: [PATCH v5 12/32] ARM: assembler: add optimized ldr/str macros to load variables from memory We will be adding variable loads to various hot paths, so it makes sense to add a helper macro that can load variables from asm code without the use of literal pool entries. On v7 or later, we can simply use MOVW/MOVT pairs, but on earlier cores, this requires a bit of hackery to emit a instruction sequence that implements this using a sequence of ADD/LDR instructions. Acked-by: Linus Walleij <linus.walleij@...aro.org> Acked-by: Nicolas Pitre <nico@...xnic.net> Signed-off-by: Ard Biesheuvel <ardb@...nel.org> Tested-by: Marc Zyngier <maz@...nel.org> Tested-by: Vladimir Murzin <vladimir.murzin@....com> # ARMv7M --- arch/arm/Kconfig | 11 +++++ arch/arm/include/asm/assembler.h | 48 ++++++++++++++++++-- 2 files changed, 55 insertions(+), 4 deletions(-) diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 99ac5d75dcec..9586636289d2 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -139,6 +139,17 @@ config ARM Europe. There is an ARM Linux project with a web page at <http://www.arm.linux.org.uk/>. +config ARM_HAS_GROUP_RELOCS + def_bool y + depends on !LD_IS_LLD || LLD_VERSION >= 140000 + depends on !COMPILE_TEST + help + Whether or not to use R_ARM_ALU_PC_Gn or R_ARM_LDR_PC_Gn group + relocations, which have been around for a long time, but were not + supported in LLD until version 14. The combined range is -/+ 256 MiB, + which is usually sufficient, but not for allyesconfig, so we disable + this feature when doing compile testing. + config ARM_HAS_SG_CHAIN bool diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h index 7d23d4bb2168..7a4e292b68e4 100644 --- a/arch/arm/include/asm/assembler.h +++ b/arch/arm/include/asm/assembler.h @@ -564,12 +564,12 @@ THUMB( orr \reg , \reg , #PSR_T_BIT ) /* * mov_l - move a constant value or [relocated] address into a register */ - .macro mov_l, dst:req, imm:req + .macro mov_l, dst:req, imm:req, cond .if __LINUX_ARM_ARCH__ < 7 - ldr \dst, =\imm + ldr\cond \dst, =\imm .else - movw \dst, #:lower16:\imm - movt \dst, #:upper16:\imm + movw\cond \dst, #:lower16:\imm + movt\cond \dst, #:upper16:\imm .endif .endm @@ -607,6 +607,46 @@ THUMB( orr \reg , \reg , #PSR_T_BIT ) __adldst_l str, \src, \sym, \tmp, \cond .endm + .macro __ldst_va, op, reg, tmp, sym, offset=0, cond +#if __LINUX_ARM_ARCH__ >= 7 || \ + !defined(CONFIG_ARM_HAS_GROUP_RELOCS) || \ + (defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS)) + mov_l \tmp, \sym, \cond +#else + /* + * Avoid a literal load, by emitting a sequence of ADD/LDR instructions + * with the appropriate relocations. The combined sequence has a range + * of -/+ 256 MiB, which should be sufficient for the core kernel and + * for modules loaded into the module region. + */ + .globl \sym + .reloc .L0_\@, R_ARM_ALU_PC_G0_NC, \sym + .reloc .L1_\@, R_ARM_ALU_PC_G1_NC, \sym + .reloc .L2_\@, R_ARM_LDR_PC_G2, \sym +.L0_\@: sub\cond \tmp, pc, #8 - \offset +.L1_\@: sub\cond \tmp, \tmp, #4 - \offset +#endif +.L2_\@: \op\cond \reg, [\tmp, #\offset] + .endm + + /* + * ldr_va - load a 32-bit word from the virtual address of \sym + */ + .macro ldr_va, rd:req, sym:req, cond, tmp, offset + .ifb \tmp + __ldst_va ldr, \rd, \rd, \sym, \offset, \cond + .else + __ldst_va ldr, \rd, \tmp, \sym, \offset, \cond + .endif + .endm + + /* + * str_va - store a 32-bit word to the virtual address of \sym + */ + .macro str_va, rn:req, sym:req, tmp:req + __ldst_va str, \rn, \tmp, \sym + .endm + /* * rev_l - byte-swap a 32-bit value * -- 2.30.2
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