linux-dev/arch/arm64/kernel/vdso/sigreturn.S, branch linus/master

arm64: vdso: Disable dwarf unwinding through the sigreturn trampoline

2020-06-23T13:47:03Z

Commit 7e9f5e6629f6 ("arm64: vdso: Add --eh-frame-hdr to ldflags") results in a .eh_frame_hdr section for the vDSO, which in turn causes the libgcc unwinder to unwind out of signal handlers using the .eh_frame information populated by our .cfi directives. In conjunction with a4eb355a3fda ("arm64: vdso: Fix CFI directives in sigreturn trampoline"), this has been shown to cause segmentation faults originating from within the unwinder during thread cancellation: | Thread 14 "virtio-net-rx" received signal SIGSEGV, Segmentation fault. | 0x0000000000435e24 in uw_frame_state_for () | (gdb) bt | #0 0x0000000000435e24 in uw_frame_state_for () | #1 0x0000000000436e88 in _Unwind_ForcedUnwind_Phase2 () | #2 0x00000000004374d8 in _Unwind_ForcedUnwind () | #3 0x0000000000428400 in __pthread_unwind (buf=) at unwind.c:121 | #4 0x0000000000429808 in __do_cancel () at ./pthreadP.h:304 | #5 sigcancel_handler (sig=32, si=0xffff33c743f0, ctx=) at nptl-init.c:200 | #6 sigcancel_handler (sig=, si=0xffff33c743f0, ctx=) at nptl-init.c:165 | #7 | #8 futex_wait_cancelable (private=0, expected=0, futex_word=0x3890b708) at ../sysdeps/unix/sysv/linux/futex-internal.h:88 After considerable bashing of heads, it appears that our CFI directives for unwinding out of the sigreturn trampoline are only processed by libgcc when both a .eh_frame_hdr section is present *and* the mysterious NOP is covered by an entry in .eh_frame. With both of these now in place, it has highlighted that our CFI directives are not comprehensive enough to restore the stack pointer of the interrupted context. This results in libgcc falling back to an arm64-specific unwinder after computing a bogus PC value from the unwind tables. The unwinder promptly dereferences this bogus address in an attempt to see if the pointed-to instruction sequence looks like the sigreturn trampoline. Restore the old unwind behaviour, which relied solely on heuristics in the unwinder, by removing the .eh_frame_hdr section from the vDSO and commenting out the insufficient CFI directives for now. Add comments to explain the current, miserable state of affairs. Cc: Tamas Zsoldos Cc: Szabolcs Nagy Cc: Catalin Marinas Cc: Daniel Kiss Acked-by: Dave Martin Reviewed-by: Vincenzo Frascino Reviewed-by: Ard Biesheuvel Reported-by: Ard Biesheuvel Signed-off-by: Will Deacon

arm64: vdso: Fix CFI directives in sigreturn trampoline

2020-05-21T11:59:26Z

Daniel reports that the .cfi_startproc is misplaced for the sigreturn trampoline, which causes LLVM's unwinder to misbehave: | I run into this with LLVM’s unwinder. | This combination was always broken. This prompted Dave to question our use of CFI directives more generally, and I ended up going down a rabbit hole trying to figure out how this very poorly documented stuff gets used. Move the CFI directives so that the "mysterious NOP" is included in the .cfi_{start,end}proc block and add a bunch of comments so that I can save myself another headache in future. Cc: Tamas Zsoldos Reported-by: Dave Martin Reported-by: Daniel Kiss Tested-by: Daniel Kiss Signed-off-by: Will Deacon

arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction

2020-05-21T11:57:18Z

For better or worse, GDB relies on the exact instruction sequence in the VDSO sigreturn trampoline in order to unwind from signals correctly. Commit c91db232da48 ("arm64: vdso: Convert to modern assembler annotations") unfortunately added a BTI C instruction to the start of __kernel_rt_sigreturn, which breaks this check. Thankfully, it's also not required, since the trampoline is called from a RET instruction when returning from the signal handler Remove the unnecessary BTI C instruction from __kernel_rt_sigreturn, and do the same for the 32-bit VDSO as well for good measure. Cc: Daniel Kiss Cc: Tamas Zsoldos Reviewed-by: Dave Martin Reviewed-by: Mark Brown Fixes: c91db232da48 ("arm64: vdso: Convert to modern assembler annotations") Signed-off-by: Will Deacon

arm64: vdso: Annotate for BTI

2020-05-07T16:53:20Z

Generate BTI annotations for all assembly files included in the 64 bit vDSO. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20200506195138.22086-10-broonie@kernel.org Signed-off-by: Will Deacon

arm64: vdso: Convert to modern assembler annotations

2020-03-09T17:36:07Z

In an effort to clarify and simplify the annotation of assembly functions new macros have been introduced. These replace ENTRY and ENDPROC with two different annotations for normal functions and those with unusual calling conventions. Convert the assembly function in the arm64 VDSO to the new macros. Signed-off-by: Mark Brown Signed-off-by: Catalin Marinas

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 234

2019-06-19T15:09:07Z

Based on 1 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation this program is distributed in the hope that it will be useful but without any warranty without even the implied warranty of merchantability or fitness for a particular purpose see the gnu general public license for more details you should have received a copy of the gnu general public license along with this program if not see http www gnu org licenses extracted by the scancode license scanner the SPDX license identifier GPL-2.0-only has been chosen to replace the boilerplate/reference in 503 file(s). Signed-off-by: Thomas Gleixner Reviewed-by: Alexios Zavras Reviewed-by: Allison Randal Reviewed-by: Enrico Weigelt Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190602204653.811534538@linutronix.de Signed-off-by: Greg Kroah-Hartman

arm64: VDSO support

2012-09-17T12:42:09Z

This patch adds VDSO support for 64-bit applications. The VDSO code is currently used for sys_rt_sigreturn() and optimised gettimeofday() (using the user-accessible generic counter). Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas Acked-by: Tony Lindgren Acked-by: Nicolas Pitre Acked-by: Olof Johansson Acked-by: Santosh Shilimkar Acked-by: Arnd Bergmann