kernel.git/arch/arm64/kernel/stacktrace.c, branch linux-5.13.y

arm64: stacktrace: avoid tracing arch_stack_walk()

2021-08-12T11:32:17Z

commit 0c32706dac1b0a72713184246952ab0f54327c21 upstream. When the function_graph tracer is in use, arch_stack_walk() may unwind the stack incorrectly, erroneously reporting itself, missing the final entry which is being traced, and reporting all traced entries between these off-by-one from where they should be. When ftrace hooks a function return, the original return address is saved to the fgraph ret_stack, and the return address in the LR (or the function's frame record) is replaced with `return_to_handler`. When arm64's unwinder encounter frames returning to `return_to_handler`, it finds the associated original return address from the fgraph ret stack, assuming the most recent `ret_to_hander` entry on the stack corresponds to the most recent entry in the fgraph ret stack, and so on. When arch_stack_walk() is used to dump the current task's stack, it starts from the caller of arch_stack_walk(). However, arch_stack_walk() can be traced, and so may push an entry on to the fgraph ret stack, leaving the fgraph ret stack offset by one from the expected position. This can be seen when dumping the stack via /proc/self/stack, where enabling the graph tracer results in an unexpected `stack_trace_save_tsk` entry at the start of the trace, and `el0_svc` missing form the end of the trace. This patch fixes this by marking arch_stack_walk() as notrace, as we do for all other functions on the path to ftrace_graph_get_ret_stack(). While a few helper functions are not marked notrace, their calls/returns are balanced, and will have no observable effect when examining the fgraph ret stack. It is possible for an exeption boundary to cause a similar offset if the return address of the interrupted context was in the LR. Fixing those cases will require some more substantial rework, and is left for subsequent patches. Before: | # cat /proc/self/stack | [<0>] proc_pid_stack+0xc4/0x140 | [<0>] proc_single_show+0x6c/0x120 | [<0>] seq_read_iter+0x240/0x4e0 | [<0>] seq_read+0xe8/0x140 | [<0>] vfs_read+0xb8/0x1e4 | [<0>] ksys_read+0x74/0x100 | [<0>] __arm64_sys_read+0x28/0x3c | [<0>] invoke_syscall+0x50/0x120 | [<0>] el0_svc_common.constprop.0+0xc4/0xd4 | [<0>] do_el0_svc+0x30/0x9c | [<0>] el0_svc+0x2c/0x54 | [<0>] el0t_64_sync_handler+0x1a8/0x1b0 | [<0>] el0t_64_sync+0x198/0x19c | # echo function_graph > /sys/kernel/tracing/current_tracer | # cat /proc/self/stack | [<0>] stack_trace_save_tsk+0xa4/0x110 | [<0>] proc_pid_stack+0xc4/0x140 | [<0>] proc_single_show+0x6c/0x120 | [<0>] seq_read_iter+0x240/0x4e0 | [<0>] seq_read+0xe8/0x140 | [<0>] vfs_read+0xb8/0x1e4 | [<0>] ksys_read+0x74/0x100 | [<0>] __arm64_sys_read+0x28/0x3c | [<0>] invoke_syscall+0x50/0x120 | [<0>] el0_svc_common.constprop.0+0xc4/0xd4 | [<0>] do_el0_svc+0x30/0x9c | [<0>] el0t_64_sync_handler+0x1a8/0x1b0 | [<0>] el0t_64_sync+0x198/0x19c After: | # cat /proc/self/stack | [<0>] proc_pid_stack+0xc4/0x140 | [<0>] proc_single_show+0x6c/0x120 | [<0>] seq_read_iter+0x240/0x4e0 | [<0>] seq_read+0xe8/0x140 | [<0>] vfs_read+0xb8/0x1e4 | [<0>] ksys_read+0x74/0x100 | [<0>] __arm64_sys_read+0x28/0x3c | [<0>] invoke_syscall+0x50/0x120 | [<0>] el0_svc_common.constprop.0+0xc4/0xd4 | [<0>] do_el0_svc+0x30/0x9c | [<0>] el0_svc+0x2c/0x54 | [<0>] el0t_64_sync_handler+0x1a8/0x1b0 | [<0>] el0t_64_sync+0x198/0x19c | # echo function_graph > /sys/kernel/tracing/current_tracer | # cat /proc/self/stack | [<0>] proc_pid_stack+0xc4/0x140 | [<0>] proc_single_show+0x6c/0x120 | [<0>] seq_read_iter+0x240/0x4e0 | [<0>] seq_read+0xe8/0x140 | [<0>] vfs_read+0xb8/0x1e4 | [<0>] ksys_read+0x74/0x100 | [<0>] __arm64_sys_read+0x28/0x3c | [<0>] invoke_syscall+0x50/0x120 | [<0>] el0_svc_common.constprop.0+0xc4/0xd4 | [<0>] do_el0_svc+0x30/0x9c | [<0>] el0_svc+0x2c/0x54 | [<0>] el0t_64_sync_handler+0x1a8/0x1b0 | [<0>] el0t_64_sync+0x198/0x19c Cc: Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Madhavan T. Venkataraman Cc: Mark Brown Cc: Will Deacon Reviwed-by: Mark Brown Link: https://lore.kernel.org/r/20210802164845.45506-3-mark.rutland@arm.com Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman

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

2021-05-07T19:11:05Z

Pull more arm64 updates from Catalin Marinas: "A mix of fixes and clean-ups that turned up too late for the first pull request: - Restore terminal stack frame records. Their previous removal caused traces which cross secondary_start_kernel to terminate one entry too late, with a spurious "0" entry. - Fix boot warning with pseudo-NMI due to the way we manipulate the PMR register. - ACPI fixes: avoid corruption of interrupt mappings on watchdog probe failure (GTDT), prevent unregistering of GIC SGIs. - Force SPARSEMEM_VMEMMAP as the only memory model, it saves with having to test all the other combinations. - Documentation fixes and updates: tagged address ABI exceptions on brk/mmap/mremap(), event stream frequency, update booting requirements on the configuration of traps" * tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: arm64: kernel: Update the stale comment arm64: Fix the documented event stream frequency arm64: entry: always set GIC_PRIO_PSR_I_SET during entry arm64: Explicitly document boot requirements for SVE arm64: Explicitly require that FPSIMD instructions do not trap arm64: Relax booting requirements for configuration of traps arm64: cpufeatures: use min and max arm64: stacktrace: restore terminal records arm64/vdso: Discard .note.gnu.property sections in vDSO arm64: doc: Add brk/mmap/mremap() to the Tagged Address ABI Exceptions psci: Remove unneeded semicolon ACPI: irq: Prevent unregistering of GIC SGIs ACPI: GTDT: Don't corrupt interrupt mappings on watchdow probe failure arm64: Show three registers per line arm64: remove HAVE_DEBUG_BUGVERBOSE arm64: alternative: simplify passing alt_region arm64: Force SPARSEMEM_VMEMMAP as the only memory management model arm64: vdso32: drop -no-integrated-as flag

arm64: stacktrace: restore terminal records

2021-04-30T17:30:45Z

We removed the terminal frame records in commit: 6106e1112cc69a36 ("arm64: remove EL0 exception frame record") ... on the assumption that as we no longer used them to find the pt_regs at exception boundaries, they were no longer necessary. However, Leo reports that as an unintended side-effect, this causes traces which cross secondary_start_kernel to terminate one entry too late, with a spurious "0" entry. There are a few ways we could sovle this, but as we're planning to use terminal records for RELIABLE_STACKTRACE, let's revert the logic change for now, keeping the update comments and accounting for the changes in commit: 3c02600144bdb0a1 ("arm64: stacktrace: Report when we reach the end of the stack") This is effectively a partial revert of commit: 6106e1112cc69a36 ("arm64: remove EL0 exception frame record") Signed-off-by: Mark Rutland Fixes: 6106e1112cc6 ("arm64: remove EL0 exception frame record") Reported-by: Leo Yan Tested-by: Leo Yan Cc: Will Deacon Cc: Mark Brown Cc: "Madhavan T. Venkataraman" Link: https://lore.kernel.org/r/20210429104813.GA33550@C02TD0UTHF1T.local Signed-off-by: Catalin Marinas

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

2021-04-26T17:25:03Z

Pull arm64 updates from Catalin Marinas: - MTE asynchronous support for KASan. Previously only synchronous (slower) mode was supported. Asynchronous is faster but does not allow precise identification of the illegal access. - Run kernel mode SIMD with softirqs disabled. This allows using NEON in softirq context for crypto performance improvements. The conditional yield support is modified to take softirqs into account and reduce the latency. - Preparatory patches for Apple M1: handle CPUs that only have the VHE mode available (host kernel running at EL2), add FIQ support. - arm64 perf updates: support for HiSilicon PA and SLLC PMU drivers, new functions for the HiSilicon HHA and L3C PMU, cleanups. - Re-introduce support for execute-only user permissions but only when the EPAN (Enhanced Privileged Access Never) architecture feature is available. - Disable fine-grained traps at boot and improve the documented boot requirements. - Support CONFIG_KASAN_VMALLOC on arm64 (only with KASAN_GENERIC). - Add hierarchical eXecute Never permissions for all page tables. - Add arm64 prctl(PR_PAC_{SET,GET}_ENABLED_KEYS) allowing user programs to control which PAC keys are enabled in a particular task. - arm64 kselftests for BTI and some improvements to the MTE tests. - Minor improvements to the compat vdso and sigpage. - Miscellaneous cleanups. * tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (86 commits) arm64/sve: Add compile time checks for SVE hooks in generic functions arm64/kernel/probes: Use BUG_ON instead of if condition followed by BUG. arm64: pac: Optimize kernel entry/exit key installation code paths arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS) arm64: mte: make the per-task SCTLR_EL1 field usable elsewhere arm64/sve: Remove redundant system_supports_sve() tests arm64: fpsimd: run kernel mode NEON with softirqs disabled arm64: assembler: introduce wxN aliases for wN registers arm64: assembler: remove conditional NEON yield macros kasan, arm64: tests supports for HW_TAGS async mode arm64: mte: Report async tag faults before suspend arm64: mte: Enable async tag check fault arm64: mte: Conditionally compile mte_enable_kernel_*() arm64: mte: Enable TCO in functions that can read beyond buffer limits kasan: Add report for async mode arm64: mte: Drop arch_enable_tagging() kasan: Add KASAN mode kernel parameter arm64: mte: Add asynchronous mode support arm64: Get rid of CONFIG_ARM64_VHE arm64: Cope with CPUs stuck in VHE mode ...

arm64: stacktrace: Move start_backtrace() out of the header

2021-03-28T17:09:47Z

Currently start_backtrace() is a static inline function in the header. Since it really shouldn't be sufficiently performance critical that we actually need to have it inlined move it into a C file, this will save anyone else scratching their head about why it is defined in the header. As far as I can see it's only there because it was factored out of the various callers. Signed-off-by: Mark Brown Acked-by: Mark Rutland Link: https://lore.kernel.org/r/20210319174022.33051-1-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64: stacktrace: don't trace arch_stack_walk()

2021-03-22T12:42:49Z

We recently converted arm64 to use arch_stack_walk() in commit: 5fc57df2f6fd ("arm64: stacktrace: Convert to ARCH_STACKWALK") The core stacktrace code expects that (when tracing the current task) arch_stack_walk() starts a trace at its caller, and does not include itself in the trace. However, arm64's arch_stack_walk() includes itself, and so traces include one more entry than callers expect. The core stacktrace code which calls arch_stack_walk() tries to skip a number of entries to prevent itself appearing in a trace, and the additional entry prevents skipping one of the core stacktrace functions, leaving this in the trace unexpectedly. We can fix this by having arm64's arch_stack_walk() begin the trace with its caller. The first value returned by the trace will be __builtin_return_address(0), i.e. the caller of arch_stack_walk(). The first frame record to be unwound will be __builtin_frame_address(1), i.e. the caller's frame record. To prevent surprises, arch_stack_walk() is also marked noinline. While __builtin_frame_address(1) is not safe in portable code, local GCC developers have confirmed that it is safe on arm64. To find the caller's frame record, the builtin can safely dereference the current function's frame record or (in theory) could stash the original FP into another GPR at function entry time, neither of which are problematic. Prior to this patch, the tracing code would unexpectedly show up in traces of the current task, e.g. | # cat /proc/self/stack | [<0>] stack_trace_save_tsk+0x98/0x100 | [<0>] proc_pid_stack+0xb4/0x130 | [<0>] proc_single_show+0x60/0x110 | [<0>] seq_read_iter+0x230/0x4d0 | [<0>] seq_read+0xdc/0x130 | [<0>] vfs_read+0xac/0x1e0 | [<0>] ksys_read+0x6c/0xfc | [<0>] __arm64_sys_read+0x20/0x30 | [<0>] el0_svc_common.constprop.0+0x60/0x120 | [<0>] do_el0_svc+0x24/0x90 | [<0>] el0_svc+0x2c/0x54 | [<0>] el0_sync_handler+0x1a4/0x1b0 | [<0>] el0_sync+0x170/0x180 After this patch, the tracing code will not show up in such traces: | # cat /proc/self/stack | [<0>] proc_pid_stack+0xb4/0x130 | [<0>] proc_single_show+0x60/0x110 | [<0>] seq_read_iter+0x230/0x4d0 | [<0>] seq_read+0xdc/0x130 | [<0>] vfs_read+0xac/0x1e0 | [<0>] ksys_read+0x6c/0xfc | [<0>] __arm64_sys_read+0x20/0x30 | [<0>] el0_svc_common.constprop.0+0x60/0x120 | [<0>] do_el0_svc+0x24/0x90 | [<0>] el0_svc+0x2c/0x54 | [<0>] el0_sync_handler+0x1a4/0x1b0 | [<0>] el0_sync+0x170/0x180 Erring on the side of caution, I've given this a spin with a bunch of toolchains, verifying the output of /proc/self/stack and checking that the assembly looked sound. For GCC (where we require version 5.1.0 or later) I tested with the kernel.org crosstool binares for versions 5.5.0, 6.4.0, 6.5.0, 7.3.0, 7.5.0, 8.1.0, 8.3.0, 8.4.0, 9.2.0, and 10.1.0. For clang (where we require version 10.0.1 or later) I tested with the llvm.org binary releases of 11.0.0, and 11.0.1. Fixes: 5fc57df2f6fd ("arm64: stacktrace: Convert to ARCH_STACKWALK") Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Chen Jun Cc: Marco Elver Cc: Mark Brown Cc: Will Deacon Cc: # 5.10.x Reviewed-by: Catalin Marinas Reviewed-by: Mark Brown Link: https://lore.kernel.org/r/20210319184106.5688-1-mark.rutland@arm.com Signed-off-by: Will Deacon

arm64: stacktrace: Report when we reach the end of the stack

2021-02-25T10:34:51Z

Currently the arm64 unwinder code returns -EINVAL whenever it can't find the next stack frame, not distinguishing between cases where the stack has been corrupted or is otherwise in a state it shouldn't be and cases where we have reached the end of the stack. At the minute none of the callers care what error code is returned but this will be important for reliable stack trace which needs to be sure that the stack is intact. Change to return -ENOENT in the case where we reach the bottom of the stack. The error codes from this function are only used in kernel, this particular code is chosen as we are indicating that we know there is no frame there. Signed-off-by: Mark Brown Acked-by: Mark Rutland Link: https://lore.kernel.org/r/20210224165037.24138-1-broonie@kernel.org Signed-off-by: Will Deacon

arm64: remove EL0 exception frame record

2021-01-20T12:47:54Z

When entering an exception from EL0, the entry code creates a synthetic frame record with a NULL PC. This was used by the code introduced in commit: 7326749801396105 ("arm64: unwind: reference pt_regs via embedded stack frame") ... to discover exception entries on the stack and dump the associated pt_regs. Since the NULL PC was undesirable for the stacktrace, we added a special case to unwind_frame() to prevent the NULL PC from being logged. Since commit: a25ffd3a6302a678 ("arm64: traps: Don't print stack or raw PC/LR values in backtraces") ... we no longer try to dump the pt_regs as part of a stacktrace, and hence no longer need the synthetic exception record. This patch removes the synthetic exception record and the associated special case in unwind_frame(). Instead, EL0 exceptions set the FP to NULL, as is the case for other terminal records (e.g. when a kernel thread starts). The synthetic record for exceptions from EL1 is retrained as this has useful unwind information for the interrupted context. To make the terminal case a bit clearer, an explicit check is added to the start of unwind_frame(). This would otherwise be caught implicitly by the on_accessible_stack() checks. Reported-by: Mark Brown Signed-off-by: Mark Rutland Signed-off-by: Mark Brown Link: https://lore.kernel.org/r/20210113173155.43063-1-broonie@kernel.org Signed-off-by: Will Deacon

arm64: Move console stack display code to stacktrace.c

2020-09-21T18:43:03Z

Currently the code for displaying a stack trace on the console is located in traps.c rather than stacktrace.c, using the unwinding code that is in stacktrace.c. This can be confusing and make the code hard to find since such output is often referred to as a stack trace which might mislead the unwary. Due to this and since traps.c doesn't interact with this code except for via the public interfaces move the code to stacktrace.c to make it easier to find. Signed-off-by: Mark Brown Link: https://lore.kernel.org/r/20200921122341.11280-1-broonie@kernel.org Signed-off-by: Will Deacon

arm64: stacktrace: Convert to ARCH_STACKWALK

2020-09-18T13:24:16Z

Historically architectures have had duplicated code in their stack trace implementations for filtering what gets traced. In order to avoid this duplication some generic code has been provided using a new interface arch_stack_walk(), enabled by selecting ARCH_STACKWALK in Kconfig, which factors all this out into the generic stack trace code. Convert arm64 to use this common infrastructure. Signed-off-by: Mark Brown Reviewed-by: Miroslav Benes Link: https://lore.kernel.org/r/20200914153409.25097-4-broonie@kernel.org Signed-off-by: Will Deacon