From: Peter Zijlstra peterz@infradead.org
commit 7c81c0c9210c9bfab2bae76aab2999de5bad27db upstream.
Commit
ee774dac0da1 ("x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()")
manages to introduce a CALL/RET pair that is before SWITCH_TO_KERNEL_CR3, which means it is before RETBleed can be mitigated.
Revert to an earlier version of the commit in Fixes. Down side is that this will bloat .text size somewhat. The alternative is fully reverting it.
The purpose of this patch was to allow migrating error_entry() to C, including the whole of kPTI. Much care needs to be taken moving that forward to not re-introduce this problem of early RETs.
Fixes: ee774dac0da1 ("x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Borislav Petkov bp@suse.de Reviewed-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Borislav Petkov bp@suse.de Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/entry/entry_64.S | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-)
--- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -317,14 +317,6 @@ SYM_CODE_END(ret_from_fork) #endif .endm
-/* Save all registers in pt_regs */ -SYM_CODE_START_LOCAL(push_and_clear_regs) - UNWIND_HINT_FUNC - PUSH_AND_CLEAR_REGS save_ret=1 - ENCODE_FRAME_POINTER 8 - RET -SYM_CODE_END(push_and_clear_regs) - /** * idtentry_body - Macro to emit code calling the C function * @cfunc: C function to be called @@ -332,8 +324,8 @@ SYM_CODE_END(push_and_clear_regs) */ .macro idtentry_body cfunc has_error_code:req
- call push_and_clear_regs - UNWIND_HINT_REGS + PUSH_AND_CLEAR_REGS + ENCODE_FRAME_POINTER
/* * Call error_entry() and switch to the task stack if from userspace.