On Tue, Sep 10, 2019 at 01:31:06pm +0100, Cristian Marussi wrote:
Add a simple fake_sigreturn testcase which builds a ucontext_t with a bad magic header and place it onto the stack. Expects a SIGSEGV on test PASS.
Introduce a common utility assembly trampoline function to invoke a sigreturn while placing the provided sigframe at wanted alignment and also an helper to make space when needed inside the sigframe reserved area.
Signed-off-by: Cristian Marussi cristian.marussi@arm.com
v5 --> v6
- fake_sigreturn: cleaned up, avoiding excessive SP misalignments
- fake_sigreturn: better formatting and prologue
- get_starting_header: cleand up and commented
- avoid timeout on failure
[...]
diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S new file mode 100644 index 000000000000..e670f8f2c8de --- /dev/null +++ b/tools/testing/selftests/arm64/signal/signals.S @@ -0,0 +1,64 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) 2019 ARM Limited */
+#include <asm/unistd.h>
+.section .rodata, "a" +call_fmt:
- .asciz "Calling sigreturn with fake sigframe sized:%zd at SP @%08lX\n"
+.text
+.globl fake_sigreturn
+/* fake_sigreturn x0:&sigframe, x1:sigframe_size, x2:misalign_bytes */ +fake_sigreturn:
- stp x29, x30, [sp, #-16]!
- mov x29, sp
- mov x20, x0
- mov x21, x1
- mov x22, x2
- /* create space on the stack for fake sigframe 16 bytes-aligned */
- add x0, x21, x22
- add x0, x0, #16
- bic x0, x0, #15 /* round_up(sigframe_size + misalign_bytes, 16) */
If I've figured this out right, x0 as computed here actually looks like round_up(sigframe_size + misalign_bytes + 1, 16) - 1.
(n + (m - 1)) & ~(m - 1) is the classic way to round up when m is a power of 2.
That's why I originally suggested to add 15. Your code works, but I think it always allocates at least one byte more than needed (?)
This is not a huge deal, and better than allocating one byte to few, but it would be good to understand whether this behaviour was intentional or not.
- sub sp, sp, x0
- add x23, sp, x22 /* new sigframe base with misaligment if any */
- ldr x0, =call_fmt
- mov x1, x21
- mov x2, x23
- bl printf
- /* memcpy the provided content, while still keeping SP aligned */
- mov x0, x23
- mov x1, x20
- mov x2, x21
- bl memcpy
- /*
* Here saving a last minute SP to current->token acts as a marker:* if we got here, we are successfully faking a sigreturn; in other* words we are sure no bad fatal signal has been raised till now* for unrelated reasons, so we should consider the possibly observed* fatal signal like SEGV coming from Kernel restore_sigframe() and* triggered as expected from our test-case.* For simplicity this assumes that current field 'token' is laid out* as first in struct tdescr*/- ldr x0, current
- str x23, [x0]
- /* finally move SP to misaligned address...if any requested */
- mov sp, x23
- mov x8, #__NR_rt_sigreturn
- svc #0
- /*
* Above sigreturn should not return...looping here leads to a timeout* and ensure proper and clean test failure, instead of jumping around* on a potentially corrupted stack.*/- b .
[...]
diff --git a/tools/testing/selftests/arm64/signal/testcases/testcases.c b/tools/testing/selftests/arm64/signal/testcases/testcases.c index 1914a01222a1..e3521949b800 100644 --- a/tools/testing/selftests/arm64/signal/testcases/testcases.c +++ b/tools/testing/selftests/arm64/signal/testcases/testcases.c @@ -148,3 +148,49 @@ bool validate_reserved(ucontext_t *uc, size_t resv_sz, char **err) return true; }
+/*
- This function walks through the records inside the provided reserved area
- trying to find enough space to fit @need_sz bytes: if not enough space is
- available and an extra_context record is present, it throws away the
- extra_context record.
- It returns a pointer to a new header where it is possible to start storing
- our need_sz bytes.
- @shead: points to the start of reserved area
- @need_sz: needed bytes
- @resv_sz: reserved area size in bytes
- @offset: if not null, this will be filled with the offset of the return
head pointer from @shead
- @return: pointer to a new head where to start storing need_sz bytes, or
NULL if space could not be made available.- */
That's much clearer now, thanks for that.
+struct _aarch64_ctx *get_starting_head(struct _aarch64_ctx *shead,
size_t need_sz, size_t resv_sz,size_t *offset)+{
[...]
Cheers ---Dave