Date: Wed, 24 Aug 2022 19:25:11 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: dc4a2d1d0e83 - main - i386: do not allow userspace to set tf_trapno on sigreturn(2) Message-ID: <202208241925.27OJPBkO069148@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=dc4a2d1d0e838579f21d9d1fef8655f902f06ab2 commit dc4a2d1d0e838579f21d9d1fef8655f902f06ab2 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2022-08-19 01:26:37 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2022-08-24 19:11:57 +0000 i386: do not allow userspace to set tf_trapno on sigreturn(2) tf_trapno is checked on return from interrupt/exception to determine if special handling is needed for switching address space. This is due to the possibility of NMI/MCHK/DBG to occur at arbitrary place in kernel, where both address space and stack used could be transient. Kernel saves current %cr3 in tf_err for such events, to restore on return. If user is able to set tf_trapno, it can trigger that special handling, and since tf_err is also user-controlled by sigreturn(2), the result is undefined. PR: 265889 Reported by: lwhsu Reviewed by: jhb Tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D36302 --- sys/i386/i386/exec_machdep.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/sys/i386/i386/exec_machdep.c b/sys/i386/i386/exec_machdep.c index 29c06ff86ca8..45921193ec94 100644 --- a/sys/i386/i386/exec_machdep.c +++ b/sys/i386/i386/exec_machdep.c @@ -640,6 +640,7 @@ osigreturn(struct thread *td, struct osigreturn_args *uap) regs->tf_esp = scp->sc_sp; regs->tf_eip = scp->sc_pc; regs->tf_eflags = eflags; + regs->tf_trapno = T_RESERVED; #if defined(COMPAT_43) if (scp->sc_onstack & 1) @@ -739,6 +740,7 @@ freebsd4_sigreturn(struct thread *td, struct freebsd4_sigreturn_args *uap) bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(*regs)); } + regs->tf_trapno = T_RESERVED; #if defined(COMPAT_43) if (ucp->uc_mcontext.mc_onstack & 1) @@ -873,6 +875,7 @@ sys_sigreturn(struct thread *td, struct sigreturn_args *uap) return (ret); bcopy(&ucp->uc_mcontext.mc_fs, regs, sizeof(*regs)); } + regs->tf_trapno = T_RESERVED; #if defined(COMPAT_43) if (ucp->uc_mcontext.mc_onstack & 1)
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