Commit 1aa2b3b7 authored by Will Deacon's avatar Will Deacon Committed by Russell King
Browse files

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
......@@ -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)
/*
......
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