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A mirror of the official Linux kernel repository just in case
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The stack_trace event is an event created by the tracing subsystem to store stack traces. It originally just contained a hard coded array of 8 words to hold the stack, and a "size" to know how many entries are there. This is exported to user space as: name: kernel_stack ID: 4 format: field:unsigned short common_type; offset:0; size:2; signed:0; field:unsigned char common_flags; offset:2; size:1; signed:0; field:unsigned char common_preempt_count; offset:3; size:1; signed:0; field:int common_pid; offset:4; size:4; signed:1; field:int size; offset:8; size:4; signed:1; field:unsigned long caller[8]; offset:16; size:64; signed:0; print fmt: "\t=> %ps\n\t=> %ps\n\t=> %ps\n" "\t=> %ps\n\t=> %ps\n\t=> %ps\n" "\t=> %ps\n\t=> %ps\n",i (void *)REC->caller[0], (void *)REC->caller[1], (void *)REC->caller[2], (void *)REC->caller[3], (void *)REC->caller[4], (void *)REC->caller[5], (void *)REC->caller[6], (void *)REC->caller[7] Where the user space tracers could parse the stack. The library was updated for this specific event to only look at the size, and not the array. But some older users still look at the array (note, the older code still checks to make sure the array fits inside the event that it read. That is, if only 4 words were saved, the parser would not read the fifth word because it will see that it was outside of the event size). This event was changed a while ago to be more dynamic, and would save a full stack even if it was greater than 8 words. It does this by simply allocating more ring buffer to hold the extra words. Then it copies in the stack via: memcpy(&entry->caller, fstack->calls, size); As the entry is struct stack_entry, that is created by a macro to both create the structure and export this to user space, it still had the caller field of entry defined as: unsigned long caller[8]. When the stack is greater than 8, the FORTIFY_SOURCE code notices that the amount being copied is greater than the source array and complains about it. It has no idea that the source is pointing to the ring buffer with the required allocation. To hide this from the FORTIFY_SOURCE logic, pointer arithmetic is used: ptr = ring_buffer_event_data(event); entry = ptr; ptr += offsetof(typeof(*entry), caller); memcpy(ptr, fstack->calls, size); Link: https://lore.kernel.org/all/20230612160748.4082850-1-svens@linux.ibm.com/ Link: https://lore.kernel.org/linux-trace-kernel/20230712105235.5fc441aa@gandalf.local.home Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Reported-by: Sven Schnelle <svens@linux.ibm.com> Tested-by: Sven Schnelle <svens@linux.ibm.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> |
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| certs | ||
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.