Patch "powerpc/rtas: use memmove for potentially overlapping buffer copy" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    powerpc/rtas: use memmove for potentially overlapping buffer copy

to the 5.10-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:
     powerpc-rtas-use-memmove-for-potentially-overlapping.patch
and it can be found in the queue-5.10 subdirectory.

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



commit d33f66b36b8581f5172308bb55cd744d70811686
Author: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
Date:   Mon Mar 6 15:33:41 2023 -0600

    powerpc/rtas: use memmove for potentially overlapping buffer copy
    
    [ Upstream commit 271208ee5e335cb1ad280d22784940daf7ddf820 ]
    
    Using memcpy() isn't safe when buf is identical to rtas_err_buf, which
    can happen during boot before slab is up. Full context which may not
    be obvious from the diff:
    
            if (altbuf) {
                    buf = altbuf;
            } else {
                    buf = rtas_err_buf;
                    if (slab_is_available())
                            buf = kmalloc(RTAS_ERROR_LOG_MAX, GFP_ATOMIC);
            }
            if (buf)
                    memcpy(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);
    
    This was found by inspection and I'm not aware of it causing problems
    in practice. It appears to have been introduced by commit
    033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel"); the
    old ppc64 version of this code did not have this problem.
    
    Use memmove() instead.
    
    Fixes: 033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel")
    Signed-off-by: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
    Reviewed-by: Andrew Donnellan <ajd@xxxxxxxxxxxxx>
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://msgid.link/20230220-rtas-queue-for-6-4-v1-2-010e4416f13f@xxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index c2e407a112a28..5976a25c6264d 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -399,7 +399,7 @@ static char *__fetch_rtas_last_error(char *altbuf)
 				buf = kmalloc(RTAS_ERROR_LOG_MAX, GFP_ATOMIC);
 		}
 		if (buf)
-			memcpy(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);
+			memmove(buf, rtas_err_buf, RTAS_ERROR_LOG_MAX);
 	}
 
 	return buf;