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x86/pkeys: Restore altstack access in sigreturn()

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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
This commit is contained in:
Aruna Ramakrishna 2024-08-02 06:13:17 +00:00 committed by Thomas Gleixner
parent 70044df250
commit d10b554919
1 changed files with 3 additions and 3 deletions
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6
arch/x86/kernel/signal_64.c
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@ -260,15 +260,15 @@ SYSCALL_DEFINE0(rt_sigreturn)
set_current_blocked(&set);
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (restore_signal_shadow_stack())
goto badframe;
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
return regs->ax;
badframe: