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x86/entry: Avoid very early RET

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commit 7c81c0c9210c9bfab2bae76aab2999de5bad27db upstream.

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  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>
This commit is contained in:
Peter Zijlstra
2022-06-14 23:15:46 +02:00
committed by Greg Kroah-Hartman
parent 1d61a29886
commit 1f068f9da7
1 changed files with 2 additions and 10 deletions
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12
arch/x86/entry/entry_64.S
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@@ -314,14 +314,6 @@ 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
@@ -329,8 +321,8 @@ 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.