kernel.git/arch/arm64/kernel/entry-ftrace.S, branch linux-6.3.y

arm64: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS

2023-01-24T11:49:43Z

This patch enables support for DYNAMIC_FTRACE_WITH_CALL_OPS on arm64. This allows each ftrace callsite to provide an ftrace_ops to the common ftrace trampoline, allowing each callsite to invoke distinct tracer functions without the need to fall back to list processing or to allocate custom trampolines for each callsite. This significantly speeds up cases where multiple distinct trace functions are used and callsites are mostly traced by a single tracer. The main idea is to place a pointer to the ftrace_ops as a literal at a fixed offset from the function entry point, which can be recovered by the common ftrace trampoline. Using a 64-bit literal avoids branch range limitations, and permits the ops to be swapped atomically without special considerations that apply to code-patching. In future this will also allow for the implementation of DYNAMIC_FTRACE_WITH_DIRECT_CALLS without branch range limitations by using additional fields in struct ftrace_ops. As noted in the core patch adding support for DYNAMIC_FTRACE_WITH_CALL_OPS, this approach allows for directly invoking ftrace_ops::func even for ftrace_ops which are dynamically-allocated (or part of a module), without going via ftrace_ops_list_func. Currently, this approach is not compatible with CLANG_CFI, as the presence/absence of pre-function NOPs changes the offset of the pre-function type hash, and there's no existing mechanism to ensure a consistent offset for instrumented and uninstrumented functions. When CLANG_CFI is enabled, the existing scheme with a global ops->func pointer is used, and there should be no functional change. I am currently working with others to allow the two to work together in future (though this will liekly require updated compiler support). I've benchamrked this with the ftrace_ops sample module [1], which is not currently upstream, but available at: https://lore.kernel.org/lkml/20230103124912.2948963-1-mark.rutland@arm.com git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git ftrace-ops-sample-20230109 Using that module I measured the total time taken for 100,000 calls to a trivial instrumented function, with a number of tracers enabled with relevant filters (which would apply to the instrumented function) and a number of tracers enabled with irrelevant filters (which would not apply to the instrumented function). I tested on an M1 MacBook Pro, running under a HVF-accelerated QEMU VM (i.e. on real hardware). Before this patch: Number of tracers || Total time | Per-call average time (ns) Relevant | Irrelevant || (ns) | Total | Overhead =========+============++=============+==============+============ 0 | 0 || 94,583 | 0.95 | - 0 | 1 || 93,709 | 0.94 | - 0 | 2 || 93,666 | 0.94 | - 0 | 10 || 93,709 | 0.94 | - 0 | 100 || 93,792 | 0.94 | - ---------+------------++-------------+--------------+------------ 1 | 1 || 6,467,833 | 64.68 | 63.73 1 | 2 || 7,509,708 | 75.10 | 74.15 1 | 10 || 23,786,792 | 237.87 | 236.92 1 | 100 || 106,432,500 | 1,064.43 | 1063.38 ---------+------------++-------------+--------------+------------ 1 | 0 || 1,431,875 | 14.32 | 13.37 2 | 0 || 6,456,334 | 64.56 | 63.62 10 | 0 || 22,717,000 | 227.17 | 226.22 100 | 0 || 103,293,667 | 1032.94 | 1031.99 ---------+------------++-------------+--------------+-------------- Note: per-call overhead is estimated relative to the baseline case with 0 relevant tracers and 0 irrelevant tracers. After this patch Number of tracers || Total time | Per-call average time (ns) Relevant | Irrelevant || (ns) | Total | Overhead =========+============++=============+==============+============ 0 | 0 || 94,541 | 0.95 | - 0 | 1 || 93,666 | 0.94 | - 0 | 2 || 93,709 | 0.94 | - 0 | 10 || 93,667 | 0.94 | - 0 | 100 || 93,792 | 0.94 | - ---------+------------++-------------+--------------+------------ 1 | 1 || 281,000 | 2.81 | 1.86 1 | 2 || 281,042 | 2.81 | 1.87 1 | 10 || 280,958 | 2.81 | 1.86 1 | 100 || 281,250 | 2.81 | 1.87 ---------+------------++-------------+--------------+------------ 1 | 0 || 280,959 | 2.81 | 1.86 2 | 0 || 6,502,708 | 65.03 | 64.08 10 | 0 || 18,681,209 | 186.81 | 185.87 100 | 0 || 103,550,458 | 1,035.50 | 1034.56 ---------+------------++-------------+--------------+------------ Note: per-call overhead is estimated relative to the baseline case with 0 relevant tracers and 0 irrelevant tracers. As can be seen from the above: a) Whenever there is a single relevant tracer function associated with a tracee, the overhead of invoking the tracer is constant, and does not scale with the number of tracers which are *not* associated with that tracee. b) The overhead for a single relevant tracer has dropped to ~1/7 of the overhead prior to this series (from 13.37ns to 1.86ns). This is largely due to permitting calls to dynamically-allocated ftrace_ops without going through ftrace_ops_list_func. I've run the ftrace selftests from v6.2-rc3, which reports: | # of passed: 110 | # of failed: 0 | # of unresolved: 3 | # of untested: 0 | # of unsupported: 0 | # of xfailed: 1 | # of undefined(test bug): 0 ... where the unresolved entries were the tests for DIRECT functions (which are not supported), and the checkbashisms selftest (which is irrelevant here): | [8] Test ftrace direct functions against tracers [UNRESOLVED] | [9] Test ftrace direct functions against kprobes [UNRESOLVED] | [62] Meta-selftest: Checkbashisms [UNRESOLVED] ... with all other tests passing (or failing as expected). Signed-off-by: Mark Rutland Cc: Florent Revest Cc: Masami Hiramatsu Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Will Deacon Link: https://lore.kernel.org/r/20230123134603.1064407-9-mark.rutland@arm.com Signed-off-by: Catalin Marinas

Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

2022-12-12T17:50:05Z

Pull arm64 updates from Will Deacon: "The highlights this time are support for dynamically enabling and disabling Clang's Shadow Call Stack at boot and a long-awaited optimisation to the way in which we handle the SVE register state on system call entry to avoid taking unnecessary traps from userspace. Summary: ACPI: - Enable FPDT support for boot-time profiling - Fix CPU PMU probing to work better with PREEMPT_RT - Update SMMUv3 MSI DeviceID parsing to latest IORT spec - APMT support for probing Arm CoreSight PMU devices CPU features: - Advertise new SVE instructions (v2.1) - Advertise range prefetch instruction - Advertise CSSC ("Common Short Sequence Compression") scalar instructions, adding things like min, max, abs, popcount - Enable DIT (Data Independent Timing) when running in the kernel - More conversion of system register fields over to the generated header CPU misfeatures: - Workaround for Cortex-A715 erratum #2645198 Dynamic SCS: - Support for dynamic shadow call stacks to allow switching at runtime between Clang's SCS implementation and the CPU's pointer authentication feature when it is supported (complete with scary DWARF parser!) Tracing and debug: - Remove static ftrace in favour of, err, dynamic ftrace! - Seperate 'struct ftrace_regs' from 'struct pt_regs' in core ftrace and existing arch code - Introduce and implement FTRACE_WITH_ARGS on arm64 to replace the old FTRACE_WITH_REGS - Extend 'crashkernel=' parameter with default value and fallback to placement above 4G physical if initial (low) allocation fails SVE: - Optimisation to avoid disabling SVE unconditionally on syscall entry and just zeroing the non-shared state on return instead Exceptions: - Rework of undefined instruction handling to avoid serialisation on global lock (this includes emulation of user accesses to the ID registers) Perf and PMU: - Support for TLP filters in Hisilicon's PCIe PMU device - Support for the DDR PMU present in Amlogic Meson G12 SoCs - Support for the terribly-named "CoreSight PMU" architecture from Arm (and Nvidia's implementation of said architecture) Misc: - Tighten up our boot protocol for systems with memory above 52 bits physical - Const-ify static keys to satisty jump label asm constraints - Trivial FFA driver cleanups in preparation for v1.1 support - Export the kernel_neon_* APIs as GPL symbols - Harden our instruction generation routines against instrumentation - A bunch of robustness improvements to our arch-specific selftests - Minor cleanups and fixes all over (kbuild, kprobes, kfence, PMU, ...)" * tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (151 commits) arm64: kprobes: Return DBG_HOOK_ERROR if kprobes can not handle a BRK arm64: kprobes: Let arch do_page_fault() fix up page fault in user handler arm64: Prohibit instrumentation on arch_stack_walk() arm64:uprobe fix the uprobe SWBP_INSN in big-endian arm64: alternatives: add __init/__initconst to some functions/variables arm_pmu: Drop redundant armpmu->map_event() in armpmu_event_init() kselftest/arm64: Allow epoll_wait() to return more than one result kselftest/arm64: Don't drain output while spawning children kselftest/arm64: Hold fp-stress children until they're all spawned arm64/sysreg: Remove duplicate definitions from asm/sysreg.h arm64/sysreg: Convert ID_DFR1_EL1 to automatic generation arm64/sysreg: Convert ID_DFR0_EL1 to automatic generation arm64/sysreg: Convert ID_AFR0_EL1 to automatic generation arm64/sysreg: Convert ID_MMFR5_EL1 to automatic generation arm64/sysreg: Convert MVFR2_EL1 to automatic generation arm64/sysreg: Convert MVFR1_EL1 to automatic generation arm64/sysreg: Convert MVFR0_EL1 to automatic generation arm64/sysreg: Convert ID_PFR2_EL1 to automatic generation arm64/sysreg: Convert ID_PFR1_EL1 to automatic generation arm64/sysreg: Convert ID_PFR0_EL1 to automatic generation ...

ftrace: arm64: remove static ftrace

2022-11-25T12:11:50Z

The build test robot pointer out that there's a build failure when: CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=y CONFIG_DYNAMIC_FTRACE_WITH_ARGS=n ... due to some mismatched ifdeffery, some of which checks CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS, and some of which checks CONFIG_DYNAMIC_FTRACE_WITH_ARGS, leading to some missing definitions expected by the core code when CONFIG_DYNAMIC_FTRACE=n and consequently CONFIG_DYNAMIC_FTRACE_WITH_ARGS=n. There's really not much point in supporting CONFIG_DYNAMIC_FTRACE=n (AKA static ftrace). All supported toolchains allow us to implement DYNAMIC_FTRACE, distributions all prefer DYNAMIC_FTRACE, and both powerpc and s390 removed support for static ftrace in commits: 0c0c52306f4792a4 ("powerpc: Only support DYNAMIC_FTRACE not static") 5d6a0163494c78ad ("s390/ftrace: enforce DYNAMIC_FTRACE if FUNCTION_TRACER is selected") ... and according to Steven, static ftrace is only supported on x86 to allow testing that the core code still functions in this configuration. Given that, let's simplify matters by removing arm64's support for static ftrace. This avoids the problem originally reported, and leaves us with less code to maintain. Fixes: 26299b3f6ba2 ("ftrace: arm64: move from REGS to ARGS") Link: https://lore.kernel.org/r/202211212249.livTPi3Y-lkp@intel.com Suggested-by: Steven Rostedt Signed-off-by: Mark Rutland Cc: Will Deacon Cc: Catalin Marinas Acked-by: Steven Rostedt (Google) Link: https://lore.kernel.org/r/20221122163624.1225912-1-mark.rutland@arm.com Signed-off-by: Will Deacon

ftrace: arm64: move from REGS to ARGS

2022-11-18T13:56:41Z

This commit replaces arm64's support for FTRACE_WITH_REGS with support for FTRACE_WITH_ARGS. This removes some overhead and complexity, and removes some latent issues with inconsistent presentation of struct pt_regs (which can only be reliably saved/restored at exception boundaries). FTRACE_WITH_REGS has been supported on arm64 since commit: 3b23e4991fb66f6d ("arm64: implement ftrace with regs") As noted in the commit message, the major reasons for implementing FTRACE_WITH_REGS were: (1) To make it possible to use the ftrace graph tracer with pointer authentication, where it's necessary to snapshot/manipulate the LR before it is signed by the instrumented function. (2) To make it possible to implement LIVEPATCH in future, where we need to hook function entry before an instrumented function manipulates the stack or argument registers. Practically speaking, we need to preserve the argument/return registers, PC, LR, and SP. Neither of these need a struct pt_regs, and only require the set of registers which are live at function call/return boundaries. Our calling convention is defined by "Procedure Call Standard for the Arm® 64-bit Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found at: https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst Per AAPCS64, all function call argument and return values are held in the following GPRs: * X0 - X7 : parameter / result registers * X8 : indirect result location register * SP : stack pointer (AKA SP) Additionally, ad function call boundaries, the following GPRs hold context/return information: * X29 : frame pointer (AKA FP) * X30 : link register (AKA LR) ... and for ftrace we need to capture the instrumented address: * PC : program counter No other GPRs are relevant, as none of the other arguments hold parameters or return values: * X9 - X17 : temporaries, may be clobbered * X18 : shadow call stack pointer (or temorary) * X19 - X28 : callee saved This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring the minimal set of registers necessary. This is always sufficient to manipulate control flow (e.g. for live-patching) or to manipulate function arguments and return values. This reduces the necessary stack usage from 336 bytes for pt_regs down to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing up 188 bytes. This could be reduced further with changes to the unwinder. As there is no longer a need to save different sets of registers for different features, we no longer need distinct `ftrace_caller` and `ftrace_regs_caller` trampolines. This allows the trampoline assembly to be simpler, and simplifies code which previously had to handle the two trampolines. I've tested this with the ftrace selftests, where there are no unexpected failures. Co-developed-by: Florent Revest Signed-off-by: Mark Rutland Signed-off-by: Florent Revest Cc: Catalin Marinas Cc: Masami Hiramatsu Cc: Steven Rostedt Cc: Will Deacon Reviewed-by: Masami Hiramatsu (Google) Reviewed-by: Steven Rostedt (Google) Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com Signed-off-by: Will Deacon

arm64: ftrace: Define ftrace_stub_graph only with FUNCTION_GRAPH_TRACER

2022-11-14T12:28:52Z

The 0-day bot reports that arm64 builds with CONFIG_CFI_CLANG + CONFIG_FTRACE are broken when CONFIG_FUNCTION_GRAPH_TRACER is not enabled: ld.lld: error: undefined symbol: __kcfi_typeid_ftrace_stub_graph >>> referenced by entry-ftrace.S:299 (arch/arm64/kernel/entry-ftrace.S:299) >>> arch/arm64/kernel/entry-ftrace.o:(.text+0x48) in archive vmlinux.a This is caused by ftrace_stub_graph using SYM_TYPE_FUNC_START when the address of the function is not taken in any C translation unit. Fix the build by only defining ftrace_stub_graph when it's actually needed, i.e. with CONFIG_FUNCTION_GRAPH_TRACER. Link: https://lore.kernel.org/lkml/202210251659.tRMs78RH-lkp@intel.com/ Fixes: 883bbbffa5a4 ("ftrace,kcfi: Separate ftrace_stub() and ftrace_stub_graph()") Reported-by: kernel test robot Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Acked-by: Mark Rutland Reviewed-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/r/20221109192831.3057131-1-samitolvanen@google.com Signed-off-by: Catalin Marinas

ftrace,kcfi: Separate ftrace_stub() and ftrace_stub_graph()

2022-10-20T15:10:27Z

Different function signatures means they needs to be different functions; otherwise CFI gets upset. As triggered by the ftrace boot tests: [] CFI failure at ftrace_return_to_handler+0xac/0x16c (target: ftrace_stub+0x0/0x14; expected type: 0x0a5d5347) Fixes: 3c516f89e17e ("x86: Add support for CONFIG_CFI_CLANG") Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Mark Rutland Tested-by: Mark Rutland Link: https://lkml.kernel.org/r/Y06dg4e1xF6JTdQq@hirez.programming.kicks-ass.net

arm64: ftrace: remove redundant label

2022-06-15T15:14:47Z

Since commit: c4a0ebf87cebbfa2 ("arm64/ftrace: Make function graph use ftrace directly") The 'ftrace_common_return' label has been unused. Remove it. Signed-off-by: Mark Rutland Cc: Chengming Zhou Cc: Will Deacon Tested-by: "Ivan T. Ivanov" Reviewed-by: Chengming Zhou Reviewed-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20220614080944.1349146-4-mark.rutland@arm.com Signed-off-by: Catalin Marinas

arm64/ftrace: Make function graph use ftrace directly

2022-04-29T18:21:12Z

As we do in commit 0c0593b45c9b ("x86/ftrace: Make function graph use ftrace directly"), we don't need special hook for graph tracer, but instead we use graph_ops:func function to install return_hooker. Since commit 3b23e4991fb6 ("arm64: implement ftrace with regs") add implementation for FTRACE_WITH_REGS on arm64, we can easily adopt the same cleanup on arm64. And this cleanup only changes the FTRACE_WITH_REGS implementation, so the mcount-based implementation is unaffected. While in theory it would be possible to make a similar cleanup for !FTRACE_WITH_REGS, this will require rework of the core code, and so for now we only change the FTRACE_WITH_REGS implementation. Tested-by: Mark Rutland Reviewed-by: Mark Rutland Signed-off-by: Chengming Zhou Link: https://lore.kernel.org/r/20220420160006.17880-2-zhouchengming@bytedance.com Signed-off-by: Catalin Marinas

arm64: Use BTI C directly and unconditionally

2021-12-14T18:12:58Z

Now we have a macro for BTI C that looks like a regular instruction change all the users of the current BTI_C macro to just emit a BTI C directly and remove the macro. This does mean that we now unconditionally BTI annotate all assembly functions, meaning that they are worse in this respect than code generated by the compiler. The overhead should be minimal for implementations with a reasonable HINT implementation. Signed-off-by: Mark Brown Reviewed-by: Ard Biesheuvel Acked-by: Mark Rutland Link: https://lore.kernel.org/r/20211214152714.2380849-4-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64: ftrace: add missing BTIs

2021-12-02T10:18:32Z

When branch target identifiers are in use, code reachable via an indirect branch requires a BTI landing pad at the branch target site. When building FTRACE_WITH_REGS atop patchable-function-entry, we miss BTIs at the start start of the `ftrace_caller` and `ftrace_regs_caller` trampolines, and when these are called from a module via a PLT (which will use a `BR X16`), we will encounter a BTI failure, e.g. | # insmod lkdtm.ko | lkdtm: No crash points registered, enable through debugfs | # echo function_graph > /sys/kernel/debug/tracing/current_tracer | # cat /sys/kernel/debug/provoke-crash/DIRECT | Unhandled 64-bit el1h sync exception on CPU0, ESR 0x34000001 -- BTI | CPU: 0 PID: 174 Comm: cat Not tainted 5.16.0-rc2-dirty #3 | Hardware name: linux,dummy-virt (DT) | pstate: 60400405 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=jc) | pc : ftrace_caller+0x0/0x3c | lr : lkdtm_debugfs_open+0xc/0x20 [lkdtm] | sp : ffff800012e43b00 | x29: ffff800012e43b00 x28: 0000000000000000 x27: ffff800012e43c88 | x26: 0000000000000000 x25: 0000000000000000 x24: ffff0000c171f200 | x23: ffff0000c27b1e00 x22: ffff0000c2265240 x21: ffff0000c23c8c30 | x20: ffff8000090ba380 x19: 0000000000000000 x18: 0000000000000000 | x17: 0000000000000000 x16: ffff80001002bb4c x15: 0000000000000000 | x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000900ff0 | x11: ffff0000c4166310 x10: ffff800012e43b00 x9 : ffff8000104f2384 | x8 : 0000000000000001 x7 : 0000000000000000 x6 : 000000000000003f | x5 : 0000000000000040 x4 : ffff800012e43af0 x3 : 0000000000000001 | x2 : ffff8000090b0000 x1 : ffff0000c171f200 x0 : ffff0000c23c8c30 | Kernel panic - not syncing: Unhandled exception | CPU: 0 PID: 174 Comm: cat Not tainted 5.16.0-rc2-dirty #3 | Hardware name: linux,dummy-virt (DT) | Call trace: | dump_backtrace+0x0/0x1a4 | show_stack+0x24/0x30 | dump_stack_lvl+0x68/0x84 | dump_stack+0x1c/0x38 | panic+0x168/0x360 | arm64_exit_nmi.isra.0+0x0/0x80 | el1h_64_sync_handler+0x68/0xd4 | el1h_64_sync+0x78/0x7c | ftrace_caller+0x0/0x3c | do_dentry_open+0x134/0x3b0 | vfs_open+0x38/0x44 | path_openat+0x89c/0xe40 | do_filp_open+0x8c/0x13c | do_sys_openat2+0xbc/0x174 | __arm64_sys_openat+0x6c/0xbc | invoke_syscall+0x50/0x120 | el0_svc_common.constprop.0+0xdc/0x100 | do_el0_svc+0x84/0xa0 | el0_svc+0x28/0x80 | el0t_64_sync_handler+0xa8/0x130 | el0t_64_sync+0x1a0/0x1a4 | SMP: stopping secondary CPUs | Kernel Offset: disabled | CPU features: 0x0,00000f42,da660c5f | Memory Limit: none | ---[ end Kernel panic - not syncing: Unhandled exception ]--- Fix this by adding the required `BTI C`, as we only require these to be reachable via BL for direct calls or BR X16/X17 for PLTs. For now, these are open-coded in the function prologue, matching the style of the `__hwasan_tag_mismatch` trampoline. In future we may wish to consider adding a new SYM_CODE_START_*() variant which has an implicit BTI. When ftrace is built atop mcount, the trampolines are marked with SYM_FUNC_START(), and so get an implicit BTI. We may need to change these over to SYM_CODE_START() in future for RELIABLE_STACKTRACE, in case we need to apply special care aroud the return address being rewritten. Fixes: 97fed779f2a6 ("arm64: bti: Provide Kconfig for kernel mode BTI") Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Mark Brown Cc: Will Deacon Reviewed-by: Mark Brown Link: https://lore.kernel.org/r/20211129135709.2274019-1-mark.rutland@arm.com Signed-off-by: Will Deacon