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Clear registers after system calls.

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This commit is contained in:
Jonas 'Sortie' Termansen 2015-05-16 19:22:46 +02:00
parent 33c7f48909
commit 0fc3d70716
3 changed files with 49 additions and 17 deletions
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4
kernel/signal.cpp
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@ -617,6 +617,7 @@ retry_another_signal:
intctx->cs = UCS | URPL;
intctx->ds = UDS | URPL;
intctx->ss = UDS | URPL;
intctx->ebx = 0;
#elif defined(__x86_64__)
intctx->rip = intctx->rdi;
intctx->rflags = intctx->rsi;
@ -624,6 +625,9 @@ retry_another_signal:
intctx->cs = UCS | URPL;
intctx->ds = UDS | URPL;
intctx->ss = UDS | URPL;
intctx->rdi = 0;
intctx->rsi = 0;
intctx->r8 = 0;
#else
#error "You may need to fix the registers"
#endif

36
kernel/x64/syscall.S
View file

@ -1,6 +1,6 @@
/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014.
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014, 2015.
This file is part of Sortix.
@ -36,9 +36,9 @@ syscall_handler:
# Make sure the requested system call is valid, if not, then fix it.
cmp $SYSCALL_MAX_NUM, %rax
jae fix_syscall
jae 3f
valid_syscall:
1:
# Read a system call function pointer.
xorq %r11, %r11
movq syscall_list(%r11,%rax,8), %rax
@ -52,19 +52,33 @@ valid_syscall:
popq %rbp
movl global_errno, %ecx
# Zero registers to avoid information leaks.
# rax is return value.
# rdi is set in a moment.
xor %rsi, %rsi
# rdx is return value (MIGHT NOT BE INITIALIZED, CAN LEAK!).
# rcx is errno.
xor %r8, %r8
xor %r9, %r9
xor %r10, %r10
xor %r11, %r11
# The rest of the registers are preserved by the ABI and syscall ABI.
# If any signals are pending, fire them now.
movq asm_signal_is_pending, %rdi
testq %rdi, %rdi
jnz call_signal_dispatcher
jnz 4f
# rdi is zero in this branch.
2:
iretq
fix_syscall:
3:
# Call the null system call instead.
xorq %rax, %rax
jmp valid_syscall
jmp 1b
call_signal_dispatcher:
4:
# We can't return to this location after the signal, since if any system
# call is made this stack will get reused and all our nice temporaries wil
# be garbage. We therefore pass the kernel the state to return to and it'll
@ -74,7 +88,11 @@ call_signal_dispatcher:
movq 24(%rsp), %r8 # userspace rsp, note %rcx is used for errno
int $130 # Deliver pending signals.
# If we end up here, it means that the signal didn't override anything and
# that we should just go ahead and return to userspace ourselves.
iretq
# that we should just go ahead and return to userspace ourselves. Zero the
# scratch registers to avoid information leaks.
xor %rdi, %rdi
xor %rsi, %rsi
xor %r8, %r8
jmp 2b
.size syscall_handler, .-syscall_handler

26
kernel/x86/syscall.S
View file

@ -1,6 +1,6 @@
/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014.
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014, 2015.
This file is part of Sortix.
@ -45,9 +45,9 @@ syscall_handler:
# Make sure the requested system call is valid.
cmp $SYSCALL_MAX_NUM, %eax
jae fix_syscall
jae 3f
valid_syscall:
1:
# Read a system call function pointer.
xorl %ebp, %ebp
movl syscall_list(%ebp,%eax,4), %eax
@ -76,19 +76,28 @@ valid_syscall:
popl %ebp
movl global_errno, %ecx
# Zero registers to avoid information leaks.
# eax is the return value.
# ecx is errno.
# edx is the return value (MIGHT NOT BE INITIALIZED, CAN LEAK!).
# ebx is set in a moment.
xor %esi, %esi
xor %edi, %edi
# If any signals are pending, fire them now.
movl asm_signal_is_pending, %ebx
testl %ebx, %ebx
jnz call_signal_dispatcher
jnz 4f
# ebx is zero in this branch.
2:
iretl
fix_syscall:
3:
# Call the null system call instead.
xorl %eax, %eax
jmp valid_syscall
jmp 1b
call_signal_dispatcher:
4:
# We can't return to this location after the signal, since if any system
# call is made this stack will get reused and all our nice temporaries wil
# be garbage. We therefore pass the kernel the state to return to and it'll
@ -97,6 +106,7 @@ call_signal_dispatcher:
int $130 # Deliver pending signals.
# If we end up here, it means that the signal didn't override anything and
# that we should just go ahead and return to userspace ourselves.
iretl
xor %ebx, %ebx
jmp 2b
.size syscall_handler, .-syscall_handler