From: Michael Ellerman Date: Mon, 9 Oct 2017 10:54:05 +0000 (+1100) Subject: powerpc: Disable the fast-endian switch syscall by default X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=727f13616c45caa72e4325c5027c1a8f41e745a9;p=linux.git powerpc: Disable the fast-endian switch syscall by default Back in 2008 we added support for "fast little-endian switch" in the syscall path. This added a special case syscall number 0x1ebe, which is caught very early in the system call exception and switches endian with as little overhead as possible. See commit 745a14cc264b ("[POWERPC] Add fast little-endian switch system call") for full details. Although it is fast, it's also completely non standard. The "syscall number" is out of the range of normal syscalls, it can't be traced or audited, and it's a bit of a wart. To the best of our knowledge it was only used by one program, now long since discontinued. So in an effort to shake out any current users, put it behind a config option, and make it default n. If anyone *is* using it they can quickly reinstate it with a rebuild, and we can flip it to default y. Signed-off-by: Michael Ellerman --- diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug index c86df246339e9..b8a1eb42a38d0 100644 --- a/arch/powerpc/Kconfig.debug +++ b/arch/powerpc/Kconfig.debug @@ -369,4 +369,10 @@ config PPC_HTDUMP def_bool y depends on PPC_PTDUMP && PPC_BOOK3S +config PPC_FAST_ENDIAN_SWITCH + bool "Deprecated fast endian-switch syscall" + depends on DEBUG_KERNEL && PPC_BOOK3S_64 + help + If you're unsure what this is, say N. + endmenu diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index acddfe79395d3..d001aa4c69a15 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -879,6 +879,7 @@ EXC_COMMON(trap_0b_common, 0xb00, unknown_exception) rfid ; \ b . ; /* prevent speculative execution */ +#ifdef CONFIG_PPC_FAST_ENDIAN_SWITCH #define SYSCALL_FASTENDIAN_TEST \ BEGIN_FTR_SECTION \ cmpdi r0,0x1ebe ; \ @@ -893,6 +894,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) \ mr r13,r9 ; \ rfid ; /* return to userspace */ \ b . ; /* prevent speculative execution */ +#else +#define SYSCALL_FASTENDIAN_TEST +#define SYSCALL_FASTENDIAN +#endif /* CONFIG_PPC_FAST_ENDIAN_SWITCH */ #if defined(CONFIG_RELOCATABLE) /*