[RESEND PATCH 0/8] Add machine check recovery when copying from user space

From: Tony Luck
Date: Wed Sep 09 2020 - 11:27:22 EST

Machine check recovery from uncorrected memory errors currently focusses
primarily on errors that are detected while running in user mode. There
is a mechanism for recovering from errors in kernel code, but it is
currently only used for memcpy_mcsafe().

The existing recover actions for errors found in user mode (unmap the
page and send SIGBUS to the task) can also be applied when the error is
found while copying data from user space to the kernel.

Roadmap to this series:

0001: Could be applied as a standalone optimization. But is essential to
this series because mce_reign() does not have access to the
saved registers from the CPU that hit the error. So it can't
recompute severity correctly for this new class of recoverable

0002: First piece of infrastructure update. Severity calculations need
access to the saved registers. So pass pointer down the call

0003: Later we need to know what type of exception handler is present
for a given kernel instruction. Rather than proliferate more
functions like ex_has_fault_handler() for each type, replace
with a function that looks up the handler and returns an enum
describing the type.

0004: Need slightly different handling for *copy_user*() faults from
get_user() faults. Create a new exception table tag and apply
to the copy functions.

0005: In fixup path of copy functions avoid dealing with the tail
when the copy took a machine check by returning that there
are no bytes left to be copied.

0006: For the REP MOVS copy case we need to check if %rsi is a user
or kernel address. There's already a static function to do this.
Make it global so x86/mce code can share the goodness.

0007: New function to get the user virtual address that was used for
a user access that hit a machine check. Add the code fragment
into do_machine_check() to take recovery actions. Does nothing
at this point because severity code to detect copy from user
case and set the kflags MCE_IN_KERNEL_COPYIN bit is in last
patch of series.

0008: Finally the keystone patch that pulls all the parts together.
An instruction decoder figures out whether an instruction
tagged as accessing user space is reading from or writing
to user space. The instructions in the switch were found
experimentally by looking at what instructions in the base
kernel are tagged in the exception table. I didn't add the
atomic operations (0x87 = XCHG etc.) that both read and write
user addresses. I think they should be safe, but I need a test
case where a futex has been poisoned to check. Probably this
switch should be expanded with all the instructions that the
compiler could possibly generate that read from user space.

Tony Luck (4):
x86/mce: Stop mce_reign() from re-computing severity for every CPU
x86/mce: Provide method to find out the type of exception handle
x86/mce: Avoid tail copy when machine check terminated a copy from
x86/mce: Decode a kernel instruction to determine if it is copying
from user

Youquan Song (4):
x86/mce: Pass pointer to saved pt_regs to severity calculation
x86/mce: Add _ASM_EXTABLE_CPY for copy user access
x86/mce: Change fault_in_kernel_space() from static to global
x86/mce: Recover from poison found while copying from user space

arch/x86/include/asm/asm.h | 6 ++
arch/x86/include/asm/extable.h | 9 ++-
arch/x86/include/asm/mce.h | 1 +
arch/x86/include/asm/traps.h | 2 +
arch/x86/kernel/cpu/mce/core.c | 89 ++++++++++++++++++++-----
arch/x86/kernel/cpu/mce/internal.h | 3 +-
arch/x86/kernel/cpu/mce/severity.c | 49 ++++++++++++--
arch/x86/lib/copy_user_64.S | 103 +++++++++++++++--------------
arch/x86/mm/extable.c | 24 +++++--
arch/x86/mm/fault.c | 2 +-
include/linux/sched.h | 1 +
11 files changed, 210 insertions(+), 79 deletions(-)