From bbd99922d0f4518518282217159666c679c6a0d1 Mon Sep 17 00:00:00 2001 From: Benjamin Gray Date: Wed, 17 Apr 2024 21:23:19 +1000 Subject: powerpc/dexcr: Reset DEXCR value across exec Inheriting the DEXCR across exec can have security and usability concerns. If a program is compiled with hash instructions it generally expects to run with NPHIE enabled. But if the parent process disables NPHIE then if it's not careful it will be disabled for any children too and the protection offered by hash checks is basically worthless. This patch introduces a per-process reset value that new execs in a particular process tree are initialized with. This enables fine grained control over what DEXCR value child processes run with by default. For example, containers running legacy binaries that expect hash instructions to act as NOPs could configure the reset value of the container root to control the default reset value for all members of the container. Signed-off-by: Benjamin Gray [mpe: Add missing SPDX tag on dexcr.c] Signed-off-by: Michael Ellerman Link: https://msgid.link/20240417112325.728010-4-bgray@linux.ibm.com --- arch/powerpc/include/asm/processor.h | 2 +- arch/powerpc/kernel/Makefile | 1 + arch/powerpc/kernel/dexcr.c | 23 +++++++++++++++++++++++ arch/powerpc/kernel/process.c | 7 +++++++ 4 files changed, 32 insertions(+), 1 deletion(-) create mode 100644 arch/powerpc/kernel/dexcr.c (limited to 'arch') diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h index 882e31296ea6..aad85a24134a 100644 --- a/arch/powerpc/include/asm/processor.h +++ b/arch/powerpc/include/asm/processor.h @@ -261,7 +261,7 @@ struct thread_struct { unsigned long sier3; unsigned long hashkeyr; unsigned long dexcr; - + unsigned long dexcr_onexec; /* Reset value to load on exec */ #endif }; diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile index d3282fbea4f2..1d183b077948 100644 --- a/arch/powerpc/kernel/Makefile +++ b/arch/powerpc/kernel/Makefile @@ -87,6 +87,7 @@ obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o obj-$(CONFIG_PPC_DAWR) += dawr.o obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_ppc970.o cpu_setup_pa6t.o obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_power.o +obj-$(CONFIG_PPC_BOOK3S_64) += dexcr.o obj-$(CONFIG_PPC_BOOK3S_64) += mce.o mce_power.o obj-$(CONFIG_PPC_BOOK3E_64) += exceptions-64e.o idle_64e.o obj-$(CONFIG_PPC_BARRIER_NOSPEC) += security.o diff --git a/arch/powerpc/kernel/dexcr.c b/arch/powerpc/kernel/dexcr.c new file mode 100644 index 000000000000..d5cd77421088 --- /dev/null +++ b/arch/powerpc/kernel/dexcr.c @@ -0,0 +1,23 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#include +#include +#include +#include +#include + +#include +#include +#include +#include + +static int __init init_task_dexcr(void) +{ + if (!early_cpu_has_feature(CPU_FTR_ARCH_31)) + return 0; + + current->thread.dexcr_onexec = mfspr(SPRN_DEXCR); + + return 0; +} +early_initcall(init_task_dexcr) diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index d482c3fd81d7..8ab779a3bdde 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1641,6 +1641,13 @@ void arch_setup_new_exec(void) current->thread.regs->amr = default_amr; current->thread.regs->iamr = default_iamr; #endif + +#ifdef CONFIG_PPC_BOOK3S_64 + if (cpu_has_feature(CPU_FTR_ARCH_31)) { + current->thread.dexcr = current->thread.dexcr_onexec; + mtspr(SPRN_DEXCR, current->thread.dexcr); + } +#endif /* CONFIG_PPC_BOOK3S_64 */ } #ifdef CONFIG_PPC64 -- cgit v1.2.3