mirror of
https://github.com/archlinuxarm/PKGBUILDs.git
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123 lines
4.3 KiB
Diff
123 lines
4.3 KiB
Diff
From 5bc061f95e03ba00911ebd2f9c1175404a5a9107 Mon Sep 17 00:00:00 2001
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From: AKASHI Takahiro <takahiro.akashi@linaro.org>
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Date: Thu, 21 Aug 2014 17:56:41 +0900
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Subject: [PATCH 08/12] arm64: ptrace: allow tracer to skip a system call
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If tracer specifies -1 as a syscall number, this traced system call should
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be skipped with a value in x0 used as a return value.
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This patch enables this semantics, but there is a restriction here:
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when syscall(-1) is issued by user, tracer cannot skip this system call
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and modify a return value at syscall entry.
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In order to ease this flavor, we need to treat whatever value in x0 as
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a return value, but this might result in a bogus value being returned,
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especially when tracer doesn't do anything at this syscall.
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So we always return ENOSYS instead, while we have another chance to change
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a return value at syscall exit.
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Please also note:
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* syscall entry tracing and syscall exit tracing (ftrace tracepoint and
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audit) are always executed, if enabled, even when skipping a system call
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(that is, -1).
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In this way, we can avoid a potential bug where audit_syscall_entry()
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might be called without audit_syscall_exit() at the previous system call
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being called, that would cause OOPs in audit_syscall_entry().
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* syscallno may also be set to -1 if a fatal signal (SIGKILL) is detected
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in tracehook_report_syscall_entry(), but since a value set to x0 (ENOSYS)
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is not used in this case, we may neglect the case.
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Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
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---
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arch/arm64/include/asm/ptrace.h | 8 ++++++++
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arch/arm64/kernel/entry.S | 4 ++++
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arch/arm64/kernel/ptrace.c | 20 ++++++++++++++++++++
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3 files changed, 32 insertions(+)
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diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
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index 300a382ed88f..8e4445719e92 100644
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--- a/arch/arm64/include/asm/ptrace.h
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+++ b/arch/arm64/include/asm/ptrace.h
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@@ -67,6 +67,14 @@
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#define COMPAT_PT_TEXT_ADDR 0x10000
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#define COMPAT_PT_DATA_ADDR 0x10004
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#define COMPAT_PT_TEXT_END_ADDR 0x10008
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+
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+/*
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+ * used to skip a system call when tracer changes its number to -1
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+ * with ptrace(PTRACE_SET_SYSCALL)
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+ */
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+#define RET_SKIP_SYSCALL -1
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+#define IS_SKIP_SYSCALL(no) ((int)(no & 0xffffffff) == -1)
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+
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#ifndef __ASSEMBLY__
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/* sizeof(struct user) for AArch32 */
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diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
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index a2cb67872c53..88fc4f84c39a 100644
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--- a/arch/arm64/kernel/entry.S
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+++ b/arch/arm64/kernel/entry.S
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@@ -25,6 +25,7 @@
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#include <asm/asm-offsets.h>
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#include <asm/errno.h>
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#include <asm/esr.h>
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+#include <asm/ptrace.h>
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#include <asm/thread_info.h>
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#include <asm/unistd.h>
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@@ -627,6 +628,8 @@ ENDPROC(el0_svc)
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__sys_trace:
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mov x0, sp
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bl syscall_trace_enter
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+ cmp w0, #RET_SKIP_SYSCALL // skip syscall?
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+ b.eq __sys_trace_return_skipped
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adr lr, __sys_trace_return // return address
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uxtw scno, w0 // syscall number (possibly new)
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mov x1, sp // pointer to regs
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@@ -641,6 +644,7 @@ __sys_trace:
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__sys_trace_return:
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str x0, [sp] // save returned x0
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+__sys_trace_return_skipped: // x0 already in regs[0]
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mov x0, sp
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bl syscall_trace_exit
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b ret_to_user
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diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
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index 6ef1e17d9c5b..b29b82576f82 100644
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--- a/arch/arm64/kernel/ptrace.c
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+++ b/arch/arm64/kernel/ptrace.c
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@@ -1137,9 +1137,29 @@ static void tracehook_report_syscall(struct pt_regs *regs,
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asmlinkage int syscall_trace_enter(struct pt_regs *regs)
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{
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+ unsigned int saved_syscallno = regs->syscallno;
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+
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if (test_thread_flag(TIF_SYSCALL_TRACE))
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tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
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+ if (IS_SKIP_SYSCALL(regs->syscallno)) {
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+ /*
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+ * RESTRICTION: we can't modify a return value of user
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+ * issued syscall(-1) here. In order to ease this flavor,
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+ * we need to treat whatever value in x0 as a return value,
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+ * but this might result in a bogus value being returned.
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+ */
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+ /*
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+ * NOTE: syscallno may also be set to -1 if fatal signal is
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+ * detected in tracehook_report_syscall_entry(), but since
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+ * a value set to x0 here is not used in this case, we may
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+ * neglect the case.
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+ */
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+ if (!test_thread_flag(TIF_SYSCALL_TRACE) ||
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+ (IS_SKIP_SYSCALL(saved_syscallno)))
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+ regs->regs[0] = -ENOSYS;
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+ }
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+
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if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
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trace_sys_enter(regs, regs->syscallno);
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--
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2.19.0
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