diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-01-11 12:11:14 +0100 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2022-01-12 16:38:25 +0100 |
| commit | 9cdbeec4096804083944d05da96bbaf59a1eb4f9 (patch) | |
| tree | 0a5f6577e801dcb928838528091f1b28d0e86b91 /arch/x86/entry/entry_32.S | |
| parent | objtool: Remove .fixup handling (diff) | |
| download | linux-9cdbeec4096804083944d05da96bbaf59a1eb4f9.tar.xz linux-9cdbeec4096804083944d05da96bbaf59a1eb4f9.zip | |
x86/entry_32: Fix segment exceptions
The LKP robot reported that commit in Fixes: caused a failure. Turns out
the ldt_gdt_32 selftest turns into an infinite loop trying to clear the
segment.
As discovered by Sean, what happens is that PARANOID_EXIT_TO_KERNEL_MODE
in the handle_exception_return path overwrites the entry stack data with
the task stack data, restoring the "bad" segment value.
Instead of having the exception retry the instruction, have it emulate
the full instruction. Replace EX_TYPE_POP_ZERO with EX_TYPE_POP_REG
which will do the equivalent of: POP %reg; MOV $imm, %reg.
In order to encode the segment registers, add them as registers 8-11 for
32-bit.
By setting regs->[defg]s the (nested) RESTORE_REGS will pop this value
at the end of the exception handler and by increasing regs->sp, it will
have skipped the stack slot.
This was debugged by Sean Christopherson <seanjc@google.com>.
[ bp: Add EX_REG_GS too. ]
Fixes: aa93e2ad7464 ("x86/entry_32: Remove .fixup usage")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/Yd1l0gInc4zRcnt/@hirez.programming.kicks-ass.net
Diffstat (limited to 'arch/x86/entry/entry_32.S')
| -rw-r--r-- | arch/x86/entry/entry_32.S | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index e0a95d8a6553..a7ec22b1d06c 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -268,11 +268,16 @@ 1: popl %ds 2: popl %es 3: popl %fs - addl $(4 + \pop), %esp /* pop the unused "gs" slot */ +4: addl $(4 + \pop), %esp /* pop the unused "gs" slot */ IRET_FRAME - _ASM_EXTABLE_TYPE(1b, 1b, EX_TYPE_POP_ZERO) - _ASM_EXTABLE_TYPE(2b, 2b, EX_TYPE_POP_ZERO) - _ASM_EXTABLE_TYPE(3b, 3b, EX_TYPE_POP_ZERO) + + /* + * There is no _ASM_EXTABLE_TYPE_REG() for ASM, however since this is + * ASM the registers are known and we can trivially hard-code them. + */ + _ASM_EXTABLE_TYPE(1b, 2b, EX_TYPE_POP_ZERO|EX_REG_DS) + _ASM_EXTABLE_TYPE(2b, 3b, EX_TYPE_POP_ZERO|EX_REG_ES) + _ASM_EXTABLE_TYPE(3b, 4b, EX_TYPE_POP_ZERO|EX_REG_FS) .endm .macro RESTORE_ALL_NMI cr3_reg:req pop=0 |