[PATCH 4.14 050/251] signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Eric W. Biederman <ebiederm@xmission.com>

commit 95bf9d646c3c3f95cb0be7e703b371db8da5be68 upstream.

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@alpha.franken.de>
Cc: Maciej Rozycki <macro@orcam.me.uk>
Cc: linux-mips@vger.kernel.org
[1] 35938a00ba86 ("MIPS: Fix ISA I FP sigcontext access violation handling")
[2] f92722dc4545 ("MIPS: Correct MIPS I FP sigcontext layout")
Cc: stable@vger.kernel.org
Fixes: f92722dc4545 ("MIPS: Correct MIPS I FP sigcontext layout")
Acked-by: Maciej W. Rozycki <macro@orcam.me.uk>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Link: https://lkml.kernel.org/r/20211020174406.17889-5-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/mips/kernel/r2300_fpu.S |    4 ++--
 arch/mips/kernel/syscall.c   |    9 ---------
 2 files changed, 2 insertions(+), 11 deletions(-)

--- 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
--- a/arch/mips/kernel/syscall.c
+++ b/arch/mips/kernel/syscall.c
@@ -233,12 +233,3 @@ SYSCALL_DEFINE3(cachectl, char *, addr,
 {
 	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);
-}