Patch "powerpc/kasan: Limit KASAN thread size increase to 32KB" 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

    powerpc/kasan: Limit KASAN thread size increase to 32KB

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:
     powerpc-kasan-limit-kasan-thread-size-increase-to-32.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 b34bc3cbd03c000a1654eedfb0bc2655eccc9c5c
Author: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Date:   Mon Feb 12 17:42:44 2024 +1100

    powerpc/kasan: Limit KASAN thread size increase to 32KB
    
    [ Upstream commit f1acb109505d983779bbb7e20a1ee6244d2b5736 ]
    
    KASAN is seen to increase stack usage, to the point that it was reported
    to lead to stack overflow on some 32-bit machines (see link).
    
    To avoid overflows the stack size was doubled for KASAN builds in
    commit 3e8635fb2e07 ("powerpc/kasan: Force thread size increase with
    KASAN").
    
    However with a 32KB stack size to begin with, the doubling leads to a
    64KB stack, which causes build errors:
      arch/powerpc/kernel/switch.S:249: Error: operand out of range (0x000000000000fe50 is not between 0xffffffffffff8000 and 0x0000000000007fff)
    
    Although the asm could be reworked, in practice a 32KB stack seems
    sufficient even for KASAN builds - the additional usage seems to be in
    the 2-3KB range for a 64-bit KASAN build.
    
    So only increase the stack for KASAN if the stack size is < 32KB.
    
    Fixes: 18f14afe2816 ("powerpc/64s: Increase default stack size to 32KB")
    Reported-by: Spoorthy <spoorthy@xxxxxxxxxxxxx>
    Reported-by: Benjamin Gray <bgray@xxxxxxxxxxxxx>
    Reviewed-by: Benjamin Gray <bgray@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/linuxppc-dev/bug-207129-206035@xxxxxxxxxxxxxxxxxxxxxxxxx%2F/
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://msgid.link/20240212064244.3924505-1-mpe@xxxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index bf5dde1a4114..15c5691dd218 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -14,7 +14,7 @@
 
 #ifdef __KERNEL__
 
-#ifdef CONFIG_KASAN
+#if defined(CONFIG_KASAN) && CONFIG_THREAD_SHIFT < 15
 #define MIN_THREAD_SHIFT	(CONFIG_THREAD_SHIFT + 1)
 #else
 #define MIN_THREAD_SHIFT	CONFIG_THREAD_SHIFT




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