Patch "objtool: Fix UNWIND_HINT_{SAVE,RESTORE} across basic blocks" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    objtool: Fix UNWIND_HINT_{SAVE,RESTORE} across basic blocks

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     objtool-fix-unwind_hint_-save-restore-across-basic-b.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 28ad3beb06726f80928ca368ec7b3d4dfdd3f4ab
Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Date:   Mon Feb 26 23:35:27 2024 -0800

    objtool: Fix UNWIND_HINT_{SAVE,RESTORE} across basic blocks
    
    [ Upstream commit 10b4c4bce3f5541f54bcc2039720b11d2bc96d79 ]
    
    If SAVE and RESTORE unwind hints are in different basic blocks, and
    objtool sees the RESTORE before the SAVE, it errors out with:
    
      vmlinux.o: warning: objtool: vmw_port_hb_in+0x242: objtool isn't smart enough to handle this CFI save/restore combo
    
    In such a case, defer following the RESTORE block until the
    straight-line path gets followed later.
    
    Fixes: 8faea26e6111 ("objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}")
    Reported-by: kernel test robot <lkp@xxxxxxxxx>
    Closes: https://lore.kernel.org/oe-kbuild-all/202402240702.zJFNmahW-lkp@xxxxxxxxx/
    Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240227073527.avcm5naavbv3cj5s@treble
    Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e308d1ba664ef..e3fc263b1b206 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3604,6 +3604,18 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 				}
 
 				if (!save_insn->visited) {
+					/*
+					 * If the restore hint insn is at the
+					 * beginning of a basic block and was
+					 * branched to from elsewhere, and the
+					 * save insn hasn't been visited yet,
+					 * defer following this branch for now.
+					 * It will be seen later via the
+					 * straight-line path.
+					 */
+					if (!prev_insn)
+						return 0;
+
 					WARN_INSN(insn, "objtool isn't smart enough to handle this CFI save/restore combo");
 					return 1;
 				}




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