Re: [PATCH 00/13] arm64: remove set_fs() and friends
flat view
From: Christoph Hellwig <hch@lst.de>
Date: 2020-09-28 07:24:42
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
On Mon, Sep 28, 2020 at 09:16:01AM +0200, Christoph Hellwig wrote:
On Fri, Sep 25, 2020 at 05:07:09PM +0100, Mark Rutland wrote:quoted
This series removes set_fs() from arm64, building atop the core rework done by Christophe. The series can be found in my arm64/set_fs-removal branch [2]. The bulk of the rework is to address the way we manipulate PAN and UAO, which is largely rendered redundant. The kernel maccess routines (__{get,put}_kernel_nofault) are trivial wrappers which share code with the uaccess routines, so I expect these should just work, but they'll need testing in-context, especially where they're wrapped by the gerneric copy routines. So far this has seen some very basic boot testing. I intend to throw Syzkaller and LTP at this soon.I'm not a an arm64 experts, but this looks reasonable to me. Also can't we remove all the remaining UAO handling as in the patch below or did I totally misunderstood how uaccess works for arm64?
Actually the patch was incomplete, here is the full one:
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6d232837cbeee8..dd3c8f8a34dae2 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig@@ -1434,27 +1434,6 @@ endmenu menu "ARMv8.2 architectural features" -config ARM64_UAO - bool "Enable support for User Access Override (UAO)" - default y - help - User Access Override (UAO; part of the ARMv8.2 Extensions) - causes the 'unprivileged' variant of the load/store instructions to - be overridden to be privileged. - - This option changes get_user() and friends to use the 'unprivileged' - variant of the load/store instructions. This ensures that user-space - really did have access to the supplied memory. When addr_limit is - set to kernel memory the UAO bit will be set, allowing privileged - access to kernel memory. - - Choosing this option will cause copy_to_user() et al to use user-space - memory permissions. - - The feature is detected at runtime, the kernel will use the - regular load/store instructions if the cpu does not implement the - feature. - config ARM64_PMEM bool "Enable support for persistent memory" select ARCH_HAS_PMEM_API
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index ef2d5a90e1815f..1c16e43f035a7a 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h@@ -29,7 +29,6 @@ static inline void init_hw_uaccess_state(void) { asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN)); - asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO)); } /*
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9ca8144f1e6a45..c460cd15dc49b3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c@@ -153,9 +153,6 @@ EXPORT_SYMBOL(cpu_hwcap_keys); } /* meta feature for alternatives */ -static bool __maybe_unused -cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused); - static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap); static bool __system_matches_cap(unsigned int n);
@@ -1763,17 +1760,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, .matches = has_no_hw_prefetch, }, -#ifdef CONFIG_ARM64_UAO - { - .desc = "User Access Override", - .capability = ARM64_HAS_UAO, - .type = ARM64_CPUCAP_SYSTEM_FEATURE, - .matches = has_cpuid_feature, - .sys_reg = SYS_ID_AA64MMFR2_EL1, - .field_pos = ID_AA64MMFR2_UAO_SHIFT, - .min_field_value = 1, - }, -#endif /* CONFIG_ARM64_UAO */ #ifdef CONFIG_ARM64_VHE { .desc = "Virtualization Host Extensions",
@@ -2701,12 +2687,6 @@ void __init setup_cpu_features(void) ARCH_DMA_MINALIGN); } -static bool __maybe_unused -cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused) -{ - return (__system_matches_cap(ARM64_HAS_PAN) && !__system_matches_cap(ARM64_HAS_UAO)); -} - static void __maybe_unused cpu_enable_cnp(struct arm64_cpu_capabilities const *cap) { cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 6ec12f4cb546f4..f223d27d991b3c 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c@@ -239,7 +239,7 @@ static void print_pstate(struct pt_regs *regs) const char *btype_str = btypes[(pstate & PSR_BTYPE_MASK) >> PSR_BTYPE_SHIFT]; - printk("pstate: %08llx (%c%c%c%c %c%c%c%c %cPAN %cUAO BTYPE=%s)\n", + printk("pstate: %08llx (%c%c%c%c %c%c%c%c %cPAN BTYPE=%s)\n", pstate, pstate & PSR_N_BIT ? 'N' : 'n', pstate & PSR_Z_BIT ? 'Z' : 'z',
@@ -250,7 +250,6 @@ static void print_pstate(struct pt_regs *regs) pstate & PSR_I_BIT ? 'I' : 'i', pstate & PSR_F_BIT ? 'F' : 'f', pstate & PSR_PAN_BIT ? '+' : '-', - pstate & PSR_UAO_BIT ? '+' : '-', btype_str); } }
@@ -417,10 +416,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, } else { memset(childregs, 0, sizeof(struct pt_regs)); childregs->pstate = PSR_MODE_EL1h; - if (IS_ENABLED(CONFIG_ARM64_UAO) && - cpus_have_const_cap(ARM64_HAS_UAO)) - childregs->pstate |= PSR_UAO_BIT; - if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE) set_ssbs_bit(childregs);
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