x86/pkeys: Restore altstack access in sigreturn()
A process can disable access to the alternate signal stack by not enabling the altstack's PKEY in the PKRU register. Nevertheless, the kernel updates the PKRU temporarily for signal handling. However, in sigreturn(), restore_sigcontext() will restore the PKRU to the user-defined PKRU value. This will cause restore_altstack() to fail with a SIGSEGV as it needs read access to the altstack which is prohibited by the user-defined PKRU value. Fix this by restoring altstack before restoring PKRU. Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/all/20240802061318.2140081-5-aruna.ramakrishna@oracle.com
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@ -260,15 +260,15 @@ SYSCALL_DEFINE0(rt_sigreturn)
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set_current_blocked(&set);
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set_current_blocked(&set);
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if (restore_altstack(&frame->uc.uc_stack))
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goto badframe;
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if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
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if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
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goto badframe;
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goto badframe;
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if (restore_signal_shadow_stack())
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if (restore_signal_shadow_stack())
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goto badframe;
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goto badframe;
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if (restore_altstack(&frame->uc.uc_stack))
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goto badframe;
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return regs->ax;
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return regs->ax;
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badframe:
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badframe:
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