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x86/mce: Decode a kernel instruction to determine if it is copying from user

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All instructions copying data between kernel and user memory
are tagged with either _ASM_EXTABLE_UA or _ASM_EXTABLE_CPY
entries in the exception table. ex_fault_handler_type() returns
EX_HANDLER_UACCESS for both of these.

Recovery is only possible when the machine check was triggered
on a read from user memory. In this case the same strategy for
recovery applies as if the user had made the access in ring3. If
the fault was in kernel memory while copying to user there is no
current recovery plan.

For MOV and MOVZ instructions a full decode of the instruction
is done to find the source address. For MOVS instructions
the source address is in the %rsi register. The function
fault_in_kernel_space() determines whether the source address is
kernel or user, upgrade it from "static" so it can be used here.

Co-developed-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201006210910.21062-7-tony.luck@intel.com
This commit is contained in:
Tony Luck
2020-10-06 14:09:10 -07:00
committed by Borislav Petkov
parent c0ab7ffce2
commit 3006381013
4 changed files with 63 additions and 5 deletions
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2
arch/x86/mm/fault.c
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@@ -1081,7 +1081,7 @@ access_error(unsigned long error_code, struct vm_area_struct *vma)
return 0;
}
static int fault_in_kernel_space(unsigned long address)
bool fault_in_kernel_space(unsigned long address)
{
/*
* On 64-bit systems, the vsyscall page is at an address above