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[PATCH] x86_64: Save/restore CS in 64bit signal handlers and force __USER_CS for CS
This allows to run 64bit signal handlers in 64bit processes that run small code snippets in compat mode. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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1 changed files with 17 additions and 0 deletions
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@ -110,6 +110,15 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, unsigned
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COPY(r14);
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COPY(r15);
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/* Kernel saves and restores only the CS segment register on signals,
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* which is the bare minimum needed to allow mixed 32/64-bit code.
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* App's signal handler can save/restore other segments if needed. */
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{
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unsigned cs;
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err |= __get_user(cs, &sc->cs);
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regs->cs = cs | 3; /* Force into user mode */
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}
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{
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unsigned int tmpflags;
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err |= __get_user(tmpflags, &sc->eflags);
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@ -187,6 +196,7 @@ setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs, unsigned lo
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{
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int err = 0;
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err |= __put_user(regs->cs, &sc->cs);
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err |= __put_user(0, &sc->gs);
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err |= __put_user(0, &sc->fs);
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@ -318,7 +328,14 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
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regs->rsp = (unsigned long)frame;
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/* Set up the CS register to run signal handlers in 64-bit mode,
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even if the handler happens to be interrupting 32-bit code. */
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regs->cs = __USER_CS;
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/* This, by contrast, has nothing to do with segment registers -
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see include/asm-x86_64/uaccess.h for details. */
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set_fs(USER_DS);
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regs->eflags &= ~TF_MASK;
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if (test_thread_flag(TIF_SINGLESTEP))
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ptrace_notify(SIGTRAP);
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