From df99da19c6c24ab65052ae1bc0904f99069478d9 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Tue, 21 Nov 2023 10:54:36 +1100 Subject: powerpc/lib: Avoid array bounds warnings in vec ops MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Building with GCC with -Warray-bounds enabled there are several warnings in sstep.c along the lines of: In function ‘do_byte_reverse’, inlined from ‘do_vec_load’ at arch/powerpc/lib/sstep.c:691:3, inlined from ‘emulate_loadstore’ at arch/powerpc/lib/sstep.c:3439:9: arch/powerpc/lib/sstep.c:289:23: error: array subscript 2 is outside array bounds of ‘u8[16]’ {aka ‘unsigned char[16]’} [-Werror=array-bounds=] 289 | up[2] = byterev_8(up[1]); | ~~~~~~^~~~~~~~~~~~~~~~~~ arch/powerpc/lib/sstep.c: In function ‘emulate_loadstore’: arch/powerpc/lib/sstep.c:681:11: note: at offset 16 into object ‘u’ of size 16 681 | } u = {}; | ^ do_byte_reverse() supports a size up to 32 bytes, but in these cases the caller is only passing a 16 byte buffer. In practice there is no bug, do_vec_load() is only called from the LOAD_VMX case in emulate_loadstore(). That in turn is only reached when analyse_instr() recognises VMX ops, and in all cases the size is no greater than 16: $ git grep -w LOAD_VMX arch/powerpc/lib/sstep.c arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 1); arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 2); arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 4); arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 16); Similarly for do_vec_store(). Although the warning is incorrect, the code would be safer if it clamped the size from the caller to the known size of the buffer. Do that using min_t(). Reported-by: Bagas Sanjaya Closes: https://lore.kernel.org/linuxppc-dev/YpbUcPrm61RLIiZF@debian.me/ Reported-by: Jan-Benedict Glaw Closes: https://lore.kernel.org/linuxppc-dev/20221212215117.aa7255t7qd6yefk4@lug-owl.de/ Reported-by: "Gustavo A. R. Silva" Closes: https://lore.kernel.org/linuxppc-dev/6a8bf78c-aedb-4d5a-b0aa-82a51a17b884@embeddedor.com/ Reviewed-by: "Gustavo A. R. Silva" Build-tested-by: "Gustavo A. R. Silva" Signed-off-by: Michael Ellerman Link: https://msgid.link/20231120235436.1569255-1-mpe@ellerman.id.au --- arch/powerpc/lib/sstep.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/powerpc/lib') diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c index a4ab8625061a..a13f05cfc7db 100644 --- a/arch/powerpc/lib/sstep.c +++ b/arch/powerpc/lib/sstep.c @@ -688,7 +688,7 @@ static nokprobe_inline int do_vec_load(int rn, unsigned long ea, if (err) return err; if (unlikely(cross_endian)) - do_byte_reverse(&u.b[ea & 0xf], size); + do_byte_reverse(&u.b[ea & 0xf], min_t(size_t, size, sizeof(u))); preempt_disable(); if (regs->msr & MSR_VEC) put_vr(rn, &u.v); @@ -719,7 +719,7 @@ static nokprobe_inline int do_vec_store(int rn, unsigned long ea, u.v = current->thread.vr_state.vr[rn]; preempt_enable(); if (unlikely(cross_endian)) - do_byte_reverse(&u.b[ea & 0xf], size); + do_byte_reverse(&u.b[ea & 0xf], min_t(size_t, size, sizeof(u))); return copy_mem_out(&u.b[ea & 0xf], ea, size, regs); } #endif /* CONFIG_ALTIVEC */ -- cgit v1.2.3