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x86/signal/64: Remove 'fs' and 'gs' from sigcontext
As far as I can tell, these fields have been set to zero on save and ignored on restore since Linux was imported into git. Rename them '__pad1' and '__pad2' to avoid confusion. This may also allow us to recycle them some day. This also adds a comment clarifying the history of those fields. I'm intentionally avoiding calling either of them '__pad0': the field formerly known as '__pad0' is now 'ss'. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Borislav Petkov <bp@alien8.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/844f8490e938780c03355be4c9b69eb4c494bf4e.1426193719.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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3 changed files with 21 additions and 6 deletions
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@ -57,8 +57,8 @@ struct sigcontext {
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unsigned long ip;
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unsigned long ip;
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unsigned long flags;
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unsigned long flags;
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unsigned short cs;
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unsigned short cs;
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unsigned short gs;
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unsigned short __pad2; /* Was called gs, but was always zero. */
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unsigned short fs;
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unsigned short __pad1; /* Was called fs, but was always zero. */
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unsigned short ss;
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unsigned short ss;
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unsigned long err;
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unsigned long err;
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unsigned long trapno;
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unsigned long trapno;
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@ -177,8 +177,23 @@ struct sigcontext {
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__u64 rip;
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__u64 rip;
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__u64 eflags; /* RFLAGS */
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__u64 eflags; /* RFLAGS */
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__u16 cs;
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__u16 cs;
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__u16 gs;
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__u16 fs;
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/*
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* Prior to 2.5.64 ("[PATCH] x86-64 updates for 2.5.64-bk3"),
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* Linux saved and restored fs and gs in these slots. This
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* was counterproductive, as fsbase and gsbase were never
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* saved, so arch_prctl was presumably unreliable.
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*
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* If these slots are ever needed for any other purpose, there
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* is some risk that very old 64-bit binaries could get
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* confused. I doubt that many such binaries still work,
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* though, since the same patch in 2.5.64 also removed the
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* 64-bit set_thread_area syscall, so it appears that there is
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* no TLS API that works in both pre- and post-2.5.64 kernels.
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*/
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__u16 __pad2; /* Was gs. */
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__u16 __pad1; /* Was fs. */
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__u16 ss;
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__u16 ss;
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__u64 err;
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__u64 err;
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__u64 trapno;
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__u64 trapno;
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@ -155,8 +155,8 @@ int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate,
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#else /* !CONFIG_X86_32 */
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#else /* !CONFIG_X86_32 */
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put_user_ex(regs->flags, &sc->flags);
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put_user_ex(regs->flags, &sc->flags);
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put_user_ex(regs->cs, &sc->cs);
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put_user_ex(regs->cs, &sc->cs);
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put_user_ex(0, &sc->gs);
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put_user_ex(0, &sc->__pad2);
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put_user_ex(0, &sc->fs);
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put_user_ex(0, &sc->__pad1);
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put_user_ex(regs->ss, &sc->ss);
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put_user_ex(regs->ss, &sc->ss);
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#endif /* CONFIG_X86_32 */
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#endif /* CONFIG_X86_32 */
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