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Peter Anvin" , "Chang S. Bae" Content-Type: text/plain; charset="UTF-8" The x86 signal frame is designed to be self-describing. The xstate_size field in the software-reserved bytes indicates the actual size of the xstate context and is used by the kernel to locate the FP_XSTATE_MAGIC2 marker during signal return. This design is required to provide portability of signal frames across different machines. For example, a process checkpointed on a system with fewer xstate features and restored on a system with more features will have a signal frame on its stack that is smaller than the destination host's default. By relying on the frame's internal xstate_size, the kernel can correctly validate and restore such frames. This series addresses a regression introduced in commit dc8aa31a7ac2 ("x86/fpu: Refine and simplify the magic number check during signal return"). Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: "Chang S. Bae" Andrei Vagin (5): Revert "x86/fpu: Refine and simplify the magic number check during signal return" x86/fpu: Document signal frame portability selftests/x86: Add a test for signal frame portability x86/fpu: Add consistency check between xstate_size and xfeatures selftests/x86: Add a consistency test for signal frames Documentation/arch/x86/xstate.rst | 14 +- arch/x86/include/uapi/asm/sigcontext.h | 13 +- arch/x86/kernel/fpu/signal.c | 36 +++- arch/x86/kernel/fpu/xstate.c | 2 +- arch/x86/kernel/fpu/xstate.h | 2 + tools/testing/selftests/x86/Makefile | 5 +- .../selftests/x86/sigframe_portability.c | 189 ++++++++++++++++++ tools/testing/selftests/x86/xstate.c | 5 - tools/testing/selftests/x86/xstate.h | 12 ++ 9 files changed, 260 insertions(+), 18 deletions(-) create mode 100644 tools/testing/selftests/x86/sigframe_portability.c -- 2.54.0.746.g67dd491aae-goog