From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
stable@vger.kernel.org,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Segher Boessenkool <segher@kernel.crashing.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 11/35] powerpc/bitops: Fix possible undefined behaviour with fls() and fls64()
Date: Mon, 4 Jan 2021 16:57:14 +0100 [thread overview]
Message-ID: <20210104155703.950803319@linuxfoundation.org> (raw)
In-Reply-To: <20210104155703.375788488@linuxfoundation.org>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
[ Upstream commit 1891ef21d92c4801ea082ee8ed478e304ddc6749 ]
fls() and fls64() are using __builtin_ctz() and _builtin_ctzll().
On powerpc, those builtins trivially use ctlzw and ctlzd power
instructions.
Allthough those instructions provide the expected result with
input argument 0, __builtin_ctz() and __builtin_ctzll() are
documented as undefined for value 0.
The easiest fix would be to use fls() and fls64() functions
defined in include/asm-generic/bitops/builtin-fls.h and
include/asm-generic/bitops/fls64.h, but GCC output is not optimal:
00000388 <testfls>:
388: 2c 03 00 00 cmpwi r3,0
38c: 41 82 00 10 beq 39c <testfls+0x14>
390: 7c 63 00 34 cntlzw r3,r3
394: 20 63 00 20 subfic r3,r3,32
398: 4e 80 00 20 blr
39c: 38 60 00 00 li r3,0
3a0: 4e 80 00 20 blr
000003b0 <testfls64>:
3b0: 2c 03 00 00 cmpwi r3,0
3b4: 40 82 00 1c bne 3d0 <testfls64+0x20>
3b8: 2f 84 00 00 cmpwi cr7,r4,0
3bc: 38 60 00 00 li r3,0
3c0: 4d 9e 00 20 beqlr cr7
3c4: 7c 83 00 34 cntlzw r3,r4
3c8: 20 63 00 20 subfic r3,r3,32
3cc: 4e 80 00 20 blr
3d0: 7c 63 00 34 cntlzw r3,r3
3d4: 20 63 00 40 subfic r3,r3,64
3d8: 4e 80 00 20 blr
When the input of fls(x) is a constant, just check x for nullity and
return either 0 or __builtin_clz(x). Otherwise, use cntlzw instruction
directly.
For fls64() on PPC64, do the same but with __builtin_clzll() and
cntlzd instruction. On PPC32, lets take the generic fls64() which
will use our fls(). The result is as expected:
00000388 <testfls>:
388: 7c 63 00 34 cntlzw r3,r3
38c: 20 63 00 20 subfic r3,r3,32
390: 4e 80 00 20 blr
000003a0 <testfls64>:
3a0: 2c 03 00 00 cmpwi r3,0
3a4: 40 82 00 10 bne 3b4 <testfls64+0x14>
3a8: 7c 83 00 34 cntlzw r3,r4
3ac: 20 63 00 20 subfic r3,r3,32
3b0: 4e 80 00 20 blr
3b4: 7c 63 00 34 cntlzw r3,r3
3b8: 20 63 00 40 subfic r3,r3,64
3bc: 4e 80 00 20 blr
Fixes: 2fcff790dcb4 ("powerpc: Use builtin functions for fls()/__fls()/fls64()")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/348c2d3f19ffcff8abe50d52513f989c4581d000.1603375524.git.christophe.leroy@csgroup.eu
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/include/asm/bitops.h | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h
index ff71566dadee5..76db1c5000bd6 100644
--- a/arch/powerpc/include/asm/bitops.h
+++ b/arch/powerpc/include/asm/bitops.h
@@ -221,15 +221,34 @@ static __inline__ void __clear_bit_unlock(int nr, volatile unsigned long *addr)
*/
static __inline__ int fls(unsigned int x)
{
- return 32 - __builtin_clz(x);
+ int lz;
+
+ if (__builtin_constant_p(x))
+ return x ? 32 - __builtin_clz(x) : 0;
+ asm("cntlzw %0,%1" : "=r" (lz) : "r" (x));
+ return 32 - lz;
}
#include <asm-generic/bitops/builtin-__fls.h>
+/*
+ * 64-bit can do this using one cntlzd (count leading zeroes doubleword)
+ * instruction; for 32-bit we use the generic version, which does two
+ * 32-bit fls calls.
+ */
+#ifdef CONFIG_PPC64
static __inline__ int fls64(__u64 x)
{
- return 64 - __builtin_clzll(x);
+ int lz;
+
+ if (__builtin_constant_p(x))
+ return x ? 64 - __builtin_clzll(x) : 0;
+ asm("cntlzd %0,%1" : "=r" (lz) : "r" (x));
+ return 64 - lz;
}
+#else
+#include <asm-generic/bitops/fls64.h>
+#endif
#ifdef CONFIG_PPC64
unsigned int __arch_hweight8(unsigned int w);
--
2.27.0
next prev parent reply other threads:[~2021-01-04 15:59 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-04 15:57 [PATCH 4.19 00/35] 4.19.165-rc1 review Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 01/35] md/raid10: initialize r10_bio->read_slot before use Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 02/35] fscrypt: add fscrypt_is_nokey_name() Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 03/35] ext4: prevent creating duplicate encrypted filenames Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 04/35] f2fs: " Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 05/35] ubifs: " Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 06/35] vfio/pci: Move dummy_resources_list init in vfio_pci_probe() Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 07/35] ext4: dont remount read-only with errors=continue on reboot Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 08/35] uapi: move constants from <linux/kernel.h> to <linux/const.h> Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 09/35] KVM: SVM: relax conditions for allowing MSR_IA32_SPEC_CTRL accesses Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 10/35] KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits Greg Kroah-Hartman
2021-01-04 15:57 ` Greg Kroah-Hartman [this message]
2021-01-04 15:57 ` [PATCH 4.19 12/35] xen/gntdev.c: Mark pages as dirty Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 13/35] null_blk: Fix zone size initialization Greg Kroah-Hartman
2021-01-06 12:54 ` Pavel Machek
2021-01-11 2:46 ` Damien Le Moal
2021-01-04 15:57 ` [PATCH 4.19 14/35] of: fix linker-section match-table corruption Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 15/35] asm-generic/tlb: Track freeing of page-table directories in struct mmu_gather Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 16/35] asm-generic/tlb: Track which levels of the page tables have been cleared Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 17/35] asm-generic/tlb, arch: Invert CONFIG_HAVE_RCU_TABLE_INVALIDATE Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 18/35] powerpc/mmu_gather: enable RCU_TABLE_FREE even for !SMP case Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 19/35] mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 20/35] asm-generic/tlb: avoid potential double flush Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 21/35] Bluetooth: hci_h5: close serdev device and free hu in h5_close Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 22/35] reiserfs: add check for an invalid ih_entry_count Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 23/35] misc: vmw_vmci: fix kernel info-leak by initializing dbells in vmci_ctx_get_chkpt_doorbells() Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 24/35] media: gp8psk: initialize stats at power control logic Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 25/35] ALSA: seq: Use bool for snd_seq_queue internal flags Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 26/35] ALSA: rawmidi: Access runtime->avail always in spinlock Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 27/35] fcntl: Fix potential deadlock in send_sig{io, urg}() Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 28/35] rtc: sun6i: Fix memleak in sun6i_rtc_clk_init Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 29/35] module: set MODULE_STATE_GOING state when a module fails to load Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 30/35] quota: Dont overflow quota file offsets Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 31/35] powerpc: sysdev: add missing iounmap() on error in mpic_msgr_probe() Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 32/35] NFSv4: Fix a pNFS layout related use-after-free race when freeing the inode Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 33/35] module: delay kobject uevent until after module init call Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 34/35] ALSA: pcm: Clear the full allocated memory at hw_params Greg Kroah-Hartman
2021-01-04 15:57 ` [PATCH 4.19 35/35] dm verity: skip verity work if I/O error when system is shutting down Greg Kroah-Hartman
2021-01-04 17:43 ` [PATCH 4.19 00/35] 4.19.165-rc1 review Daniel Díaz
2021-01-05 9:06 ` Greg Kroah-Hartman
2021-01-04 19:59 ` Pavel Machek
2021-01-05 1:58 ` Guenter Roeck
2021-01-05 9:06 ` Greg Kroah-Hartman
2021-01-05 16:44 ` Shuah Khan
2021-01-06 13:46 ` Greg Kroah-Hartman
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