On Mon, Dec 04, 2023 at 09:22:28AM -0700, Nathan Chancellor wrote:
On Sun, Dec 03, 2023 at 03:23:53PM -0500, Sasha Levin wrote:This is a note to let you know that I've just added the patch titled arm64: Restrict CPU_BIG_ENDIAN to GNU as or LLVM IAS 15.x or newer to the 4.19-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: arm64-restrict-cpu_big_endian-to-gnu-as-or-llvm-ias-.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 4c762ee5a651ad98e47860959d05a8cb18248bdf Author: Nathan Chancellor <nathan@xxxxxxxxxx> Date: Wed Oct 25 10:21:28 2023 -0700 arm64: Restrict CPU_BIG_ENDIAN to GNU as or LLVM IAS 15.x or newer [ Upstream commit 146a15b873353f8ac28dc281c139ff611a3c4848 ] Prior to LLVM 15.0.0, LLVM's integrated assembler would incorrectly byte-swap NOP when compiling for big-endian, and the resulting series of bytes happened to match the encoding of FNMADD S21, S30, S0, S0. This went unnoticed until commit: 34f66c4c4d5518c1 ("arm64: Use a positive cpucap for FP/SIMD") Prior to that commit, the kernel would always enable the use of FPSIMD early in boot when __cpu_setup() initialized CPACR_EL1, and so usage of FNMADD within the kernel was not detected, but could result in the corruption of user or kernel FPSIMD state. After that commit, the instructions happen to trap during boot prior to FPSIMD being detected and enabled, e.g. | Unhandled 64-bit el1h sync exception on CPU0, ESR 0x000000001fe00000 -- ASIMD | CPU: 0 PID: 0 Comm: swapper Not tainted 6.6.0-rc3-00013-g34f66c4c4d55 #1 | Hardware name: linux,dummy-virt (DT) | pstate: 400000c9 (nZcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) | pc : __pi_strcmp+0x1c/0x150 | lr : populate_properties+0xe4/0x254 | sp : ffffd014173d3ad0 | x29: ffffd014173d3af0 x28: fffffbfffddffcb8 x27: 0000000000000000 | x26: 0000000000000058 x25: fffffbfffddfe054 x24: 0000000000000008 | x23: fffffbfffddfe000 x22: fffffbfffddfe000 x21: fffffbfffddfe044 | x20: ffffd014173d3b70 x19: 0000000000000001 x18: 0000000000000005 | x17: 0000000000000010 x16: 0000000000000000 x15: 00000000413e7000 | x14: 0000000000000000 x13: 0000000000001bcc x12: 0000000000000000 | x11: 00000000d00dfeed x10: ffffd414193f2cd0 x9 : 0000000000000000 | x8 : 0101010101010101 x7 : ffffffffffffffc0 x6 : 0000000000000000 | x5 : 0000000000000000 x4 : 0101010101010101 x3 : 000000000000002a | x2 : 0000000000000001 x1 : ffffd014171f2988 x0 : fffffbfffddffcb8 | Kernel panic - not syncing: Unhandled exception | CPU: 0 PID: 0 Comm: swapper Not tainted 6.6.0-rc3-00013-g34f66c4c4d55 #1 | Hardware name: linux,dummy-virt (DT) | Call trace: | dump_backtrace+0xec/0x108 | show_stack+0x18/0x2c | dump_stack_lvl+0x50/0x68 | dump_stack+0x18/0x24 | panic+0x13c/0x340 | el1t_64_irq_handler+0x0/0x1c | el1_abort+0x0/0x5c | el1h_64_sync+0x64/0x68 | __pi_strcmp+0x1c/0x150 | unflatten_dt_nodes+0x1e8/0x2d8 | __unflatten_device_tree+0x5c/0x15c | unflatten_device_tree+0x38/0x50 | setup_arch+0x164/0x1e0 | start_kernel+0x64/0x38c | __primary_switched+0xbc/0xc4 Restrict CONFIG_CPU_BIG_ENDIAN to a known good assembler, which is either GNU as or LLVM's IAS 15.0.0 and newer, which contains the linked commit. Closes: https://github.com/ClangBuiltLinux/linux/issues/1948 Link: https://github.com/llvm/llvm-project/commit/1379b150991f70a5782e9a143c2ba5308da1161c Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Link: https://lore.kernel.org/r/20231025-disable-arm64-be-ias-b4-llvm-15-v1-1-b25263ed8b23@xxxxxxxxxx Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 92646f12a66d2..ff8e0db1693e9 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -759,6 +759,8 @@ choice config CPU_BIG_ENDIAN bool "Build big-endian kernel" depends on !LD_IS_LLD || LLD_VERSION >= 130000 + # https://github.com/llvm/llvm-project/commit/1379b150991f70a5782e9a143c2ba5308da1161c + depends on AS_IS_GNU || AS_VERSION >= 150000Both this backport and the backport of commit e9c6deee00e9 ("arm64: Make CPU_BIG_ENDIAN depend on ld.bfd or ld.lld 13.0.0+") are incorrect for 5.4 and 4.19, which do not have CONFIG_AS_IS_GNU, CONFIG_AS_VERSION, or CONFIG_LLD_VERSION. I don't think this patch is worth pursuing in 5.4 and 4.19, I would be very surprised if someone was to hit this issue there, as arm64 big endian is pretty esoteric as is. If someone does report something at some point, we can consider it then but for now, I think they should be dropped from 5.4 and 4.19.
Dropped from 5.4 and 4.19, thanks! -- Thanks, Sasha
