5.10-stable review patch. If anyone has any objections, please let me know.
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From: Mark Rutland mark.rutland@arm.com
commit 61d64a376ea80f9097e7ea599bcd68671b836dc6 upstream.
In general, exceptions taken from EL1 need to be handled separately from exceptions taken from EL0, as the logic to handle the two cases can be significantly divergent, and exceptions taken from EL1 typically have more stringent requirements on locking and instrumentation.
Subsequent patches will rework the way EL1 UNDEFs are handled in order to address longstanding soundness issues with instrumentation and RCU. In preparation for that rework, this patch splits the existing do_undefinstr() handler into separate do_el0_undef() and do_el1_undef() handlers.
Prior to this patch, do_undefinstr() was marked with NOKPROBE_SYMBOL(), preventing instrumentation via kprobes. However, do_undefinstr() invokes other code which can be instrumented, and:
* For UNDEFINED exceptions taken from EL0, there is no risk of recursion within kprobes. Therefore it is safe for do_el0_undef to be instrumented with kprobes, and it does not need to be marked with NOKPROBE_SYMBOL().
* For UNDEFINED exceptions taken from EL1, either:
(a) The exception is has been taken when manipulating SSBS; these cases are limited and do not occur within code that can be invoked recursively via kprobes. Hence, in these cases instrumentation with kprobes is benign.
(b) The exception has been taken for an unknown reason, as other than manipulating SSBS we do not expect to take UNDEFINED exceptions from EL1. Any handling of these exception is best-effort.
... and in either case, marking do_el1_undef() with NOKPROBE_SYMBOL() isn't sufficient to prevent recursion via kprobes as functions it calls (including die()) are instrumentable via kprobes.
Hence, it's not worthwhile to mark do_el1_undef() with NOKPROBE_SYMBOL(). The same applies to do_el1_bti() and do_el1_fpac(), so their NOKPROBE_SYMBOL() annotations are also removed.
Aside from the new instrumentability, there should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: James Morse james.morse@arm.com Cc: Joey Gouly joey.gouly@arm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Will Deacon will@kernel.org Link: https://lore.kernel.org/r/20221019144123.612388-3-mark.rutland@arm.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Jinjie Ruan ruanjinjie@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/exception.h | 3 ++- arch/arm64/kernel/entry-common.c | 4 ++-- arch/arm64/kernel/traps.c | 22 ++++++++++++---------- 3 files changed, 16 insertions(+), 13 deletions(-)
--- a/arch/arm64/include/asm/exception.h +++ b/arch/arm64/include/asm/exception.h @@ -33,7 +33,8 @@ asmlinkage void exit_to_user_mode(void); void arm64_enter_nmi(struct pt_regs *regs); void arm64_exit_nmi(struct pt_regs *regs); void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs); -void do_undefinstr(struct pt_regs *regs, unsigned long esr); +void do_el0_undef(struct pt_regs *regs, unsigned long esr); +void do_el1_undef(struct pt_regs *regs, unsigned long esr); void do_el0_bti(struct pt_regs *regs); void do_el1_bti(struct pt_regs *regs, unsigned long esr); asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr); --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -136,7 +136,7 @@ static void noinstr el1_undef(struct pt_ { enter_from_kernel_mode(regs); local_daif_inherit(regs); - do_undefinstr(regs, esr); + do_el1_undef(regs, esr); local_daif_mask(); exit_to_kernel_mode(regs); } @@ -332,7 +332,7 @@ static void noinstr el0_undef(struct pt_ { enter_from_user_mode(); local_daif_restore(DAIF_PROCCTX); - do_undefinstr(regs, esr); + do_el0_undef(regs, esr); }
static void noinstr el0_bti(struct pt_regs *regs) --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -395,7 +395,7 @@ void arm64_notify_segfault(unsigned long force_signal_inject(SIGSEGV, code, addr, 0); }
-void do_undefinstr(struct pt_regs *regs, unsigned long esr) +void do_el0_undef(struct pt_regs *regs, unsigned long esr) { /* check for AArch32 breakpoint instructions */ if (!aarch32_break_handler(regs)) @@ -404,12 +404,16 @@ void do_undefinstr(struct pt_regs *regs, if (call_undef_hook(regs) == 0) return;
- if (!user_mode(regs)) - die("Oops - Undefined instruction", regs, esr); - force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc, 0); } -NOKPROBE_SYMBOL(do_undefinstr); + +void do_el1_undef(struct pt_regs *regs, unsigned long esr) +{ + if (call_undef_hook(regs) == 0) + return; + + die("Oops - Undefined instruction", regs, esr); +}
void do_el0_bti(struct pt_regs *regs) { @@ -420,7 +424,6 @@ void do_el1_bti(struct pt_regs *regs, un { die("Oops - BTI", regs, esr); } -NOKPROBE_SYMBOL(do_el1_bti);
void do_el0_fpac(struct pt_regs *regs, unsigned long esr) { @@ -435,7 +438,6 @@ void do_el1_fpac(struct pt_regs *regs, u */ die("Oops - FPAC", regs, esr); } -NOKPROBE_SYMBOL(do_el1_fpac);
#define __user_cache_maint(insn, address, res) \ if (address >= user_addr_max()) { \ @@ -671,7 +673,7 @@ void do_el0_cp15(unsigned long esr, stru hook_base = cp15_64_hooks; break; default: - do_undefinstr(regs, esr); + do_el0_undef(regs, esr); return; }
@@ -686,7 +688,7 @@ void do_el0_cp15(unsigned long esr, stru * EL0. Fall back to our usual undefined instruction handler * so that we handle these consistently. */ - do_undefinstr(regs, esr); + do_el0_undef(regs, esr); } #endif
@@ -705,7 +707,7 @@ void do_el0_sys(unsigned long esr, struc * back to our usual undefined instruction handler so that we handle * these consistently. */ - do_undefinstr(regs, esr); + do_el0_undef(regs, esr); }
static const char *esr_class_str[] = {