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Commit 1aa2b3b7 authored by Will Deacon's avatar Will Deacon Committed by Russell King
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ARM: 7748/1: oabi: handle faults when loading swi instruction from userspace 



Running an OABI_COMPAT kernel on an SMP platform can lead to fun and
games with page aging.

If one CPU issues a swi instruction immediately before another CPU
decides to mkold the page containing the swi instruction, then we will
fault attempting to load the instruction during the vector_swi handler
in order to retrieve its immediate field. Since this fault is not
currently dealt with by our exception tables, this results in a panic:

  Unable to handle kernel paging request at virtual address 4020841c
  pgd = c490c000
  [4020841c] *pgd=84451831, *pte=bf05859d, *ppte=00000000
  Internal error: Oops: 17 [#1] PREEMPT SMP ARM
  Modules linked in: hid_sony(O)
  CPU: 1    Tainted: G        W  O  (3.4.0-perf-gf496dca-01162-gcbcc62b #1)
  PC is at vector_swi+0x28/0x88
  LR is at 0x40208420

This patch wraps all of the swi instruction loads with the USER macro
and provides a shared exception table entry which simply rewinds the
saved user PC and returns from the system call (without setting tbl, so
there's no worries with tracing or syscall restarting). Returning to
userspace will re-enter the page fault handler, from where we will
probably send SIGSEGV to the current task.

Reported-by: default avatarWang, Yalin <yalin.wang@sonymobile.com>
Reviewed-by: default avatarNicolas Pitre <nico@linaro.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 81f28946

arch/arm/kernel/entry-common.S

+29 −13
Original line number Diff line number Diff line
@@ -362,6 +362,16 @@ ENTRY(vector_swi) 
	str	r0, [sp, #S_OLD_R0]		@ Save OLD_R0

	zero_fp



#ifdef CONFIG_ALIGNMENT_TRAP

	ldr	ip, __cr_alignment

	ldr	ip, [ip]

	mcr	p15, 0, ip, c1, c0		@ update control register

#endif



	enable_irq

	ct_user_exit

	get_thread_info tsk



	/*

	 * Get the system call number.

	 */
@@ -375,9 +385,9 @@ ENTRY(vector_swi) 
#ifdef CONFIG_ARM_THUMB

	tst	r8, #PSR_T_BIT

	movne	r10, #0				@ no thumb OABI emulation

	ldreq	r10, [lr, #-4]			@ get SWI instruction

 USER(	ldreq	r10, [lr, #-4]		)	@ get SWI instruction

#else

	ldr	r10, [lr, #-4]			@ get SWI instruction

 USER(	ldr	r10, [lr, #-4]		)	@ get SWI instruction

#endif

#ifdef CONFIG_CPU_ENDIAN_BE8

	rev	r10, r10			@ little endian instruction
@@ -392,22 +402,13 @@ ENTRY(vector_swi) 
	/* Legacy ABI only, possibly thumb mode. */

	tst	r8, #PSR_T_BIT			@ this is SPSR from save_user_regs

	addne	scno, r7, #__NR_SYSCALL_BASE	@ put OS number in

	ldreq	scno, [lr, #-4]

 USER(	ldreq	scno, [lr, #-4]		)



#else

	/* Legacy ABI only. */

	ldr	scno, [lr, #-4]			@ get SWI instruction

 USER(	ldr	scno, [lr, #-4]		)	@ get SWI instruction

#endif



#ifdef CONFIG_ALIGNMENT_TRAP

	ldr	ip, __cr_alignment

	ldr	ip, [ip]

	mcr	p15, 0, ip, c1, c0		@ update control register

#endif

	enable_irq

	ct_user_exit



	get_thread_info tsk

	adr	tbl, sys_call_table		@ load syscall table pointer



#if defined(CONFIG_OABI_COMPAT)
@@ -442,6 +443,21 @@ local_restart: 
	eor	r0, scno, #__NR_SYSCALL_BASE	@ put OS number back

	bcs	arm_syscall	

	b	sys_ni_syscall			@ not private func



#if defined(CONFIG_OABI_COMPAT) || !defined(CONFIG_AEABI)

	/*

	 * We failed to handle a fault trying to access the page

	 * containing the swi instruction, but we're not really in a

	 * position to return -EFAULT. Instead, return back to the

	 * instruction and re-enter the user fault handling path trying

	 * to page it in. This will likely result in sending SEGV to the

	 * current task.

	 */

9001:

	sub	lr, lr, #4

	str	lr, [sp, #S_PC]

	b	ret_fast_syscall

#endif

ENDPROC(vector_swi)



	/*