linux-kernel - [PATCH 05/20] signal/mips: Update (_save|_restore)_fp

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Message-Id: <20211020174406.17889-5-ebiederm@xmission.com>
Date:   Wed, 20 Oct 2021 12:43:51 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Maciej Rozycki <macro@...am.me.uk>, linux-mips@...r.kernel.org
Subject: [PATCH 05/20] signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT

When an instruction to save or restore a register from the stack fails
in _save_fp_context or _restore_fp_context return with -EFAULT.  This
change was made to r2300_fpu.S[1] but it looks like it got lost with
the introduction of EX2[2].  This is also what the other implementation
of _save_fp_context and _restore_fp_context in r4k_fpu.S does, and
what is needed for the callers to be able to handle the error.

Furthermore calling do_exit(SIGSEGV) from bad_stack is wrong because
it does not terminate the entire process it just terminates a single
thread.

As the changed code was the only caller of arch/mips/kernel/syscall.c:bad_stack
remove the problematic and now unused helper function.

Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Maciej Rozycki <macro@...am.me.uk>
Cc: linux-mips@...r.kernel.org
[1] 35938a00ba86 ("MIPS: Fix ISA I FP sigcontext access violation handling")
[2] f92722dc4545 ("MIPS: Correct MIPS I FP sigcontext layout")
Fixes: f92722dc4545 ("MIPS: Correct MIPS I FP sigcontext layout")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 arch/mips/kernel/r2300_fpu.S | 4 ++--
 arch/mips/kernel/syscall.c   | 9 ---------
 2 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/arch/mips/kernel/r2300_fpu.S b/arch/mips/kernel/r2300_fpu.S
index 12e58053544f..cbf6db98cfb3 100644
--- a/arch/mips/kernel/r2300_fpu.S
+++ b/arch/mips/kernel/r2300_fpu.S
@@ -29,8 +29,8 @@
 #define EX2(a,b)						\
 9:	a,##b;							\
 	.section __ex_table,"a";				\
-	PTR	9b,bad_stack;					\
-	PTR	9b+4,bad_stack;					\
+	PTR	9b,fault;					\
+	PTR	9b+4,fault;					\
 	.previous
 
 	.set	mips1
diff --git a/arch/mips/kernel/syscall.c b/arch/mips/kernel/syscall.c
index 2afa3eef486a..5512cd586e6e 100644
--- a/arch/mips/kernel/syscall.c
+++ b/arch/mips/kernel/syscall.c
@@ -240,12 +240,3 @@ SYSCALL_DEFINE3(cachectl, char *, addr, int, nbytes, int, op)
 {
 	return -ENOSYS;
 }
-
-/*
- * If we ever come here the user sp is bad.  Zap the process right away.
- * Due to the bad stack signaling wouldn't work.
- */
-asmlinkage void bad_stack(void)
-{
-	do_exit(SIGSEGV);
-}
-- 
2.20.1