arm64: uaccess: remove set_fs() (3d2403fd) · Commits · 戴 / test

Now that the uaccess primitives dont take addr_limit into account, we have no need to manipulate this via set_fs() and get_fs(). Remove support for these, along with some infrastructure this renders redundant. We no longer need to flip UAO to access kernel memory under KERNEL_DS, and head.S unconditionally clears UAO for all kernel configurations via an ERET in init_kernel_el. Thus, we don't need to dynamically flip UAO, nor do we need to context-switch it. However, we still need to adjust PAN during SDEI entry. Masking of __user pointers no longer needs to use the dynamic value of addr_limit, and can use a constant derived from the maximum possible userspace task size. A new TASK_SIZE_MAX constant is introduced for this, which is also used by core code. In configurations supporting 52-bit VAs, this may include a region of unusable VA space above a 48-bit TTBR0 limit, but never includes any portion of TTBR1. Note that TASK_SIZE_MAX is an exclusive limit, while USER_DS and KERNEL_DS were inclusive limits, and is converted to a mask by subtracting one. As the SDEI entry code repurposes the otherwise unnecessary pt_regs::orig_addr_limit field to store the TTBR1 of the interrupted context, for now we rename that to pt_regs::sdei_ttbr1. In future we can consider factoring that out. Signed-off-by:

Mark Rutland <mark.rutland@arm.com> Acked-by:

James Morse <james.morse@arm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201202131558.39270-10-mark.rutland@arm.com Signed-off-by:

Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

+0 −1

Original line number	Diff line number	Diff line
		@@ -195,7 +195,6 @@ config ARM64
		select PCI_SYSCALL if PCI
		select POWER_RESET
		select POWER_SUPPLY
		select SET_FS
		select SPARSE_IRQ
		select SWIOTLB
		select SYSCTL_EXCEPTION_TRACE

arch/arm64/include/asm/exec.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -10,6 +10,5 @@
		#include <linux/sched.h>

		extern unsigned long arch_align_stack(unsigned long sp);
		void uao_thread_switch(struct task_struct *next);

		#endif /* __ASM_EXEC_H */

arch/arm64/include/asm/processor.h

+1 −3

Original line number	Diff line number	Diff line
		@@ -8,9 +8,6 @@
		#ifndef __ASM_PROCESSOR_H
		#define __ASM_PROCESSOR_H

		#define KERNEL_DS UL(-1)
		#define USER_DS ((UL(1) << VA_BITS) - 1)

		/*
		* On arm64 systems, unaligned accesses by the CPU are cheap, and so there is
		* no point in shifting all network buffers by 2 bytes just to make some IP
		@@ -48,6 +45,7 @@

		#define DEFAULT_MAP_WINDOW_64 (UL(1) << VA_BITS_MIN)
		#define TASK_SIZE_64 (UL(1) << vabits_actual)
		#define TASK_SIZE_MAX (UL(1) << VA_BITS)

		#ifdef CONFIG_COMPAT
		#if defined(CONFIG_ARM64_64K_PAGES) && defined(CONFIG_KUSER_HELPERS)

arch/arm64/include/asm/ptrace.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -193,8 +193,7 @@ struct pt_regs {
		s32 syscallno;
		u32 unused2;
		#endif

		u64 orig_addr_limit;
		u64 sdei_ttbr1;
		/* Only valid when ARM64_HAS_IRQ_PRIO_MASKING is enabled. */
		u64 pmr_save;
		u64 stackframe[2];

arch/arm64/include/asm/thread_info.h

+0 −4

Original line number	Diff line number	Diff line
		@@ -18,14 +18,11 @@ struct task_struct;
		#include <asm/stack_pointer.h>
		#include <asm/types.h>

		typedef unsigned long mm_segment_t;

		/*
		* low level task data that entry.S needs immediate access to.
		*/
		struct thread_info {
		unsigned long flags; /* low level flags */
		mm_segment_t addr_limit; /* address limit */
		#ifdef CONFIG_ARM64_SW_TTBR0_PAN
		u64 ttbr0; /* saved TTBR0_EL1 */
		#endif
		@@ -119,7 +116,6 @@ void arch_release_task_struct(struct task_struct *tsk);
		{ \
		.flags = _TIF_FOREIGN_FPSTATE, \
		.preempt_count = INIT_PREEMPT_COUNT, \
		.addr_limit = KERNEL_DS, \
		INIT_SCS \
		}

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