On Mon, Jul 08, 2024 at 06:51:52PM +0300, Kalle Valo wrote: > Kees Cook <kees@xxxxxxxxxx> writes: > > > On Thu, Jul 04, 2024 at 05:43:41PM +0300, Kalle Valo wrote: > >> From: Kalle Valo <quic_kvalo@xxxxxxxxxxx> > >> > >> Johannes reported with GCC 11.4 there's a fortify warning below. The warning is > >> not seen with GCC 12.1 nor 13.2. Weirdly moving the other operand of sum to the > >> other side the warning goes away. This is safe to do as the value of the > >> operand is check earlier. But the code looks worse with this so I'm not sure > >> what to do. > > > > FWIW, this isn't fortify, but -Wrestrict. > > Ah, thanks for correcting. I just saw fortify-string.h and made the > wrong assumption. > > > I would expect the same warnings even with CONFIG_FORTIFY_SOURCE > > disabled. Regardless, it's worth figuring out what's going on. It > > looks like this is GCC's value range tracker deciding it sees a way > > for things to go weird. > > > > I suspect they fixed -Wrestrict in later GCC versions. It might need to > > be version-limited... > > > >> In file included from ./include/linux/string.h:374, > >> from ./include/linux/bitmap.h:13, > >> from ./include/linux/cpumask.h:13, > >> from ./include/linux/sched.h:16, > >> from ./include/linux/delay.h:23, > >> from drivers/net/wireless/ath/ath12k/wow.c:7: > >> drivers/net/wireless/ath/ath12k/wow.c: In function > >> ‘ath12k_wow_convert_8023_to_80211.constprop’: > >> ./include/linux/fortify-string.h:114:33: error: ‘__builtin_memcpy’ > >> accessing 18446744073709551611 or more bytes at offsets 0 and 0 > >> overlaps 9223372036854775799 bytes at offset -9223372036854775804 > >> [-Werror=restrict] > > > > These huge negative values imply to me that GCC is looking at some > > signed values somewhere. > > > >> [...] > >> diff --git a/drivers/net/wireless/ath/ath12k/wow.c b/drivers/net/wireless/ath/ath12k/wow.c > >> index c5cba825a84a..e9588bb7561c 100644 > >> --- a/drivers/net/wireless/ath/ath12k/wow.c > >> +++ b/drivers/net/wireless/ath/ath12k/wow.c > >> @@ -186,7 +186,7 @@ ath12k_wow_convert_8023_to_80211(struct ath12k *ar, > >> if (eth_pkt_ofs < ETH_ALEN) { > >> pkt_ofs = eth_pkt_ofs + a1_ofs; > >> > >> - if (eth_pkt_ofs + eth_pat_len < ETH_ALEN) { > >> + if (eth_pat_len < ETH_ALEN - eth_pkt_ofs) { > >> memcpy(pat, eth_pat, eth_pat_len); > >> memcpy(bytemask, eth_bytemask, eth_pat_len); > > > > Both eth_pkt_ofs and eth_pat_len are size_t. ETH_ALEN isn't, but it > > would be promoted to size_t here. The value tracker should see that > > eth_pkt_ofs could be [0..ETH_ALEN). eth_pat_len is coming from an "int", > > though, so that might be the confusion. It may think eth_pat_len could > > be [0..UINT_MAX] (i.e. the full range of int within size_t). > > > > So [0..ETH_ALEN) + [0..UINT_MAX] < 6 might be doing something wrong in > > GCC 11.x, and it's not actually doing the size_t promotion correctly, > > or deciding something has wrapped and then thinking eth_pat_len could > > span a giant region of the address space, which freaks out -Wrestrict. > > i.e. it's seeing that for the "if" to be true, eth_pat_len could be large > > enough to wrap around the addition (though this shouldn't be possible > > for 64-bit size_t). > > > > So I could see how [0..UINT_MAX] < 6 - [0..ETH_ALEN) would make it > > happier: the right side is now [1..6], so eth_pat_len becomes [1..6). > > Earlier I did some testing and I noticed that this if test also gives a > warning: > > 1 + eth_pat_len < ETH_ALEN > > But this doesn't have any warning: > > 0 + eth_pat_len < ETH_ALEN > > And I stopped my investigation there :) > > > Reviewed-by: Kees Cook <kees@xxxxxxxxxx> > > So you think this should be applied? It's not really logical so I would > prefer to avoid taking it if possible. Or should we just ignore the > warning? It only happens on GCC 11 anyway. I suspect this won't be the only place in the kernel where -Wrestrict will give weird results with GCC 11, and there are still plenty of folks using GCC 11. I think the best option would probably be to version-check GCC to gate the addition of -Wrestrict. Arnd, what do you think? This looks like a more extreme version of commit f9fc1ec28bae ("crypto: drivers - avoid memcpy size warning") -Kees -- Kees Cook