From ed975485a13d1f6080218aa71c29425ba2dfb332 Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Tue, 11 Feb 2025 18:22:30 +0000 Subject: [PATCH 1/2] MIPS: Export syscall stack arguments properly for remote use We have several places across the kernel where we want to access another task's syscall arguments, such as ptrace(2), seccomp(2), etc., by making a call to syscall_get_arguments(). This works for register arguments right away by accessing the task's `regs' member of `struct pt_regs', however for stack arguments seen with 32-bit/o32 kernels things are more complicated. Technically they ought to be obtained from the user stack with calls to an access_remote_vm(), but we have an easier way available already. So as to be able to access syscall stack arguments as regular function arguments following the MIPS calling convention we copy them over from the user stack to the kernel stack in arch/mips/kernel/scall32-o32.S, in handle_sys(), to the current stack frame's outgoing argument space at the top of the stack, which is where the handler called expects to see its incoming arguments. This area is also pointed at by the `pt_regs' pointer obtained by task_pt_regs(). Make the o32 stack argument space a proper member of `struct pt_regs' then, by renaming the existing member from `pad0' to `args' and using generated offsets to access the space. No functional change though. With the change in place the o32 kernel stack frame layout at the entry to a syscall handler invoked by handle_sys() is therefore as follows: $sp + 68 -> | ... | <- pt_regs.regs[9] +---------------------+ $sp + 64 -> | $t0 | <- pt_regs.regs[8] +---------------------+ $sp + 60 -> | $a3/argument #4 | <- pt_regs.regs[7] +---------------------+ $sp + 56 -> | $a2/argument #3 | <- pt_regs.regs[6] +---------------------+ $sp + 52 -> | $a1/argument #2 | <- pt_regs.regs[5] +---------------------+ $sp + 48 -> | $a0/argument #1 | <- pt_regs.regs[4] +---------------------+ $sp + 44 -> | $v1 | <- pt_regs.regs[3] +---------------------+ $sp + 40 -> | $v0 | <- pt_regs.regs[2] +---------------------+ $sp + 36 -> | $at | <- pt_regs.regs[1] +---------------------+ $sp + 32 -> | $zero | <- pt_regs.regs[0] +---------------------+ $sp + 28 -> | stack argument #8 | <- pt_regs.args[7] +---------------------+ $sp + 24 -> | stack argument #7 | <- pt_regs.args[6] +---------------------+ $sp + 20 -> | stack argument #6 | <- pt_regs.args[5] +---------------------+ $sp + 16 -> | stack argument #5 | <- pt_regs.args[4] +---------------------+ $sp + 12 -> | psABI space for $a3 | <- pt_regs.args[3] +---------------------+ $sp + 8 -> | psABI space for $a2 | <- pt_regs.args[2] +---------------------+ $sp + 4 -> | psABI space for $a1 | <- pt_regs.args[1] +---------------------+ $sp + 0 -> | psABI space for $a0 | <- pt_regs.args[0] +---------------------+ holding user data received and with the first 4 frame slots reserved by the psABI for the compiler to spill the incoming arguments from $a0-$a3 registers (which it sometimes does according to its needs) and the next 4 frame slots designated by the psABI for any stack function arguments that follow. This data is also available for other tasks to peek/poke at as reqired and where permitted. Signed-off-by: Maciej W. Rozycki Signed-off-by: Thomas Bogendoerfer --- arch/mips/include/asm/ptrace.h | 4 ++-- arch/mips/kernel/asm-offsets.c | 6 ++++++ arch/mips/kernel/scall32-o32.S | 8 ++++---- 3 files changed, 12 insertions(+), 6 deletions(-) diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h index 4a2b40ce39e0..85fa9962266a 100644 --- a/arch/mips/include/asm/ptrace.h +++ b/arch/mips/include/asm/ptrace.h @@ -27,8 +27,8 @@ */ struct pt_regs { #ifdef CONFIG_32BIT - /* Pad bytes for argument save space on the stack. */ - unsigned long pad0[8]; + /* Saved syscall stack arguments; entries 0-3 unused. */ + unsigned long args[8]; #endif /* Saved main processor registers. */ diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c index cb1045ebab06..b910ec54a3a1 100644 --- a/arch/mips/kernel/asm-offsets.c +++ b/arch/mips/kernel/asm-offsets.c @@ -27,6 +27,12 @@ void output_ptreg_defines(void); void output_ptreg_defines(void) { COMMENT("MIPS pt_regs offsets."); +#ifdef CONFIG_32BIT + OFFSET(PT_ARG4, pt_regs, args[4]); + OFFSET(PT_ARG5, pt_regs, args[5]); + OFFSET(PT_ARG6, pt_regs, args[6]); + OFFSET(PT_ARG7, pt_regs, args[7]); +#endif OFFSET(PT_R0, pt_regs, regs[0]); OFFSET(PT_R1, pt_regs, regs[1]); OFFSET(PT_R2, pt_regs, regs[2]); diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S index 2c604717e630..4947a4f39e37 100644 --- a/arch/mips/kernel/scall32-o32.S +++ b/arch/mips/kernel/scall32-o32.S @@ -64,10 +64,10 @@ load_a6: user_lw(t7, 24(t0)) # argument #7 from usp load_a7: user_lw(t8, 28(t0)) # argument #8 from usp loads_done: - sw t5, 16(sp) # argument #5 to ksp - sw t6, 20(sp) # argument #6 to ksp - sw t7, 24(sp) # argument #7 to ksp - sw t8, 28(sp) # argument #8 to ksp + sw t5, PT_ARG4(sp) # argument #5 to ksp + sw t6, PT_ARG5(sp) # argument #6 to ksp + sw t7, PT_ARG6(sp) # argument #7 to ksp + sw t8, PT_ARG7(sp) # argument #8 to ksp .set pop .section __ex_table,"a" From 733a90561ad0a4a74035d2d627098da85d43b592 Mon Sep 17 00:00:00 2001 From: "Dmitry V. Levin" Date: Wed, 12 Feb 2025 01:02:09 +0200 Subject: [PATCH 2/2] MIPS: fix mips_get_syscall_arg() for o32 This makes ptrace/get_syscall_info selftest pass on mips o32 and mips64 o32 by fixing the following two test assertions: 1. get_syscall_info test assertion on mips o32: # get_syscall_info.c:218:get_syscall_info:Expected exp_args[5] (3134521044) == info.entry.args[4] (4911432) # get_syscall_info.c:219:get_syscall_info:wait #1: entry stop mismatch 2. get_syscall_info test assertion on mips64 o32: # get_syscall_info.c:209:get_syscall_info:Expected exp_args[2] (3134324433) == info.entry.args[1] (18446744072548908753) # get_syscall_info.c:210:get_syscall_info:wait #1: entry stop mismatch The first assertion happens due to mips_get_syscall_arg() trying to access another task's context but failing to do it properly because get_user() it calls just peeks at the current task's context. It usually does not crash because the default user stack always gets assigned the same VMA, but it is pure luck which mips_get_syscall_arg() wouldn't have if e.g. the stack was switched (via setcontext(3) or however) or a non-default process's thread peeked at, and in any case irrelevant data is obtained just as observed with the test case. mips_get_syscall_arg() ought to be using access_remote_vm() instead to retrieve the other task's stack contents, but given that the data has been already obtained and saved in `struct pt_regs' it would be an overkill. The first assertion is fixed for mips o32 by using struct pt_regs.args instead of get_user() to obtain syscall arguments. This approach works due to this piece in arch/mips/kernel/scall32-o32.S: /* * Ok, copy the args from the luser stack to the kernel stack. */ .set push .set noreorder .set nomacro load_a4: user_lw(t5, 16(t0)) # argument #5 from usp load_a5: user_lw(t6, 20(t0)) # argument #6 from usp load_a6: user_lw(t7, 24(t0)) # argument #7 from usp load_a7: user_lw(t8, 28(t0)) # argument #8 from usp loads_done: sw t5, PT_ARG4(sp) # argument #5 to ksp sw t6, PT_ARG5(sp) # argument #6 to ksp sw t7, PT_ARG6(sp) # argument #7 to ksp sw t8, PT_ARG7(sp) # argument #8 to ksp .set pop .section __ex_table,"a" PTR_WD load_a4, bad_stack_a4 PTR_WD load_a5, bad_stack_a5 PTR_WD load_a6, bad_stack_a6 PTR_WD load_a7, bad_stack_a7 .previous arch/mips/kernel/scall64-o32.S has analogous code for mips64 o32 that allows fixing the issue by obtaining syscall arguments from struct pt_regs.regs[4..11] instead of the erroneous use of get_user(). The second assertion is fixed by truncating 64-bit values to 32-bit syscall arguments. Fixes: c0ff3c53d4f9 ("MIPS: Enable HAVE_ARCH_TRACEHOOK.") Signed-off-by: Dmitry V. Levin Signed-off-by: Thomas Bogendoerfer --- arch/mips/include/asm/syscall.h | 32 ++++++++------------------------ 1 file changed, 8 insertions(+), 24 deletions(-) diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h index ebdf4d910af2..056aa1b713e2 100644 --- a/arch/mips/include/asm/syscall.h +++ b/arch/mips/include/asm/syscall.h @@ -57,37 +57,21 @@ static inline void mips_syscall_update_nr(struct task_struct *task, static inline void mips_get_syscall_arg(unsigned long *arg, struct task_struct *task, struct pt_regs *regs, unsigned int n) { - unsigned long usp __maybe_unused = regs->regs[29]; - +#ifdef CONFIG_32BIT switch (n) { case 0: case 1: case 2: case 3: *arg = regs->regs[4 + n]; - return; - -#ifdef CONFIG_32BIT case 4: case 5: case 6: case 7: - get_user(*arg, (int *)usp + n); + *arg = regs->args[n]; return; -#endif - -#ifdef CONFIG_64BIT - case 4: case 5: case 6: case 7: -#ifdef CONFIG_MIPS32_O32 - if (test_tsk_thread_flag(task, TIF_32BIT_REGS)) - get_user(*arg, (int *)usp + n); - else -#endif - *arg = regs->regs[4 + n]; - - return; -#endif - - default: - BUG(); } - - unreachable(); +#else + *arg = regs->regs[4 + n]; + if ((IS_ENABLED(CONFIG_MIPS32_O32) && + test_tsk_thread_flag(task, TIF_32BIT_REGS))) + *arg = (unsigned int)*arg; +#endif } static inline long syscall_get_error(struct task_struct *task,