Re: [PATCH] powerpc/32s: Fix shift-out-of-bounds in KASAN init
From: Erhard F. <hidden>
Date: 2021-11-30 13:45:55
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On Tue, 30 Nov 2021 09:42:37 +0100 Christophe Leroy [off-list ref] wrote:
quoted hunk ↗ jump to hunk
================================================================================ UBSAN: shift-out-of-bounds in arch/powerpc/mm/kasan/book3s_32.c:22:23 shift exponent -1 is negative CPU: 0 PID: 0 Comm: swapper Not tainted 5.15.5-gentoo-PowerMacG4 #9 Call Trace: [c214be60] [c0ba0048] dump_stack_lvl+0x80/0xb0 (unreliable) [c214be80] [c0b99288] ubsan_epilogue+0x10/0x5c [c214be90] [c0b98fe0] __ubsan_handle_shift_out_of_bounds+0x94/0x138 [c214bf00] [c1c0f010] kasan_init_region+0xd8/0x26c [c214bf30] [c1c0ed84] kasan_init+0xc0/0x198 [c214bf70] [c1c08024] setup_arch+0x18/0x54c [c214bfc0] [c1c037f0] start_kernel+0x90/0x33c [c214bff0] [00003610] 0x3610 ================================================================================ This happens when the directly mapped memory is a power of 2. Fix it by checking the shift and set the result to 0 when shift is -1 Reported-by: Erhard Furtner <redacted> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215169 Fixes: 7974c4732642 ("powerpc/32s: Implement dedicated kasan_init_region()") Signed-off-by: Christophe Leroy <redacted> --- arch/powerpc/mm/kasan/book3s_32.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/arch/powerpc/mm/kasan/book3s_32.c b/arch/powerpc/mm/kasan/book3s_32.c index 202bd260a009..35b287b0a8da 100644 --- a/arch/powerpc/mm/kasan/book3s_32.c +++ b/arch/powerpc/mm/kasan/book3s_32.c@@ -19,7 +19,8 @@ int __init kasan_init_region(void *start, size_t size) block = memblock_alloc(k_size, k_size_base); if (block && k_size_base >= SZ_128K && k_start == ALIGN(k_start, k_size_base)) { - int k_size_more = 1 << (ffs(k_size - k_size_base) - 1); + int shift = ffs(k_size - k_size_base); + int k_size_more = shift ? 1 << (shift - 1) : 0; setbat(-1, k_start, __pa(block), k_size_base, PAGE_KERNEL); if (k_size_more >= SZ_128K)-- 2.33.1
Tested Christophes patch applied on 5.15.5 which works fine. Thanks! I'll close the bugzilla report once it gets into stable. Regards Erhard