6c25da5ad5
This is a second attempt to make the improvements from c6f2062935
("x86/signal/64: Fix SS handling for signals delivered to 64-bit
programs"), which was reverted by 51adbfbba5c6 ("x86/signal/64: Add
support for SS in the 64-bit signal context").
This adds two new uc_flags flags. UC_SIGCONTEXT_SS will be set for
all 64-bit signals (including x32). It indicates that the saved SS
field is valid and that the kernel supports the new behavior.
The goal is to fix a problems with signal handling in 64-bit tasks:
SS wasn't saved in the 64-bit signal context, making it awkward to
determine what SS was at the time of signal delivery and making it
impossible to return to a non-flat SS (as calling sigreturn clobbers
SS).
This also made it extremely difficult for 64-bit tasks to return to
fully-defined 16-bit contexts, because only the kernel can easily do
espfix64, but sigreturn was unable to set a non-flag SS:ESP.
(DOSEMU has a monstrous hack to partially work around this
limitation.)
If we could go back in time, the correct fix would be to make 64-bit
signals work just like 32-bit signals with respect to SS: save it
in signal context, reset it when delivering a signal, and restore
it in sigreturn.
Unfortunately, doing that (as I tried originally) breaks DOSEMU:
DOSEMU wouldn't reset the signal context's SS when clearing the LDT
and changing the saved CS to 64-bit mode, since it predates the SS
context field existing in the first place.
This patch is a bit more complicated, and it tries to balance a
bunch of goals. It makes most cases of changing ucontext->ss during
signal handling work as expected.
I do this by special-casing the interesting case. On sigreturn,
ucontext->ss will be honored by default, unless the ucontext was
created from scratch by an old program and had a 64-bit CS
(unfortunately, CRIU can do this) or was the result of changing a
32-bit signal context to 64-bit without resetting SS (as DOSEMU
does).
For the benefit of new 64-bit software that uses segmentation (new
versions of DOSEMU might), the new behavior can be detected with a
new ucontext flag UC_SIGCONTEXT_SS.
To avoid compilation issues, __pad0 is left as an alias for ss in
ucontext.
The nitty-gritty details are documented in the header file.
This patch also re-enables the sigreturn_64 and ldt_gdt_64 selftests,
as the kernel change allows both of them to pass.
Tested-by: Stas Sergeev <stsp@list.ru>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/749149cbfc3e75cd7fcdad69a854b399d792cc6f.1455664054.git.luto@kernel.org
[ Small readability edit. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
75 lines
2.3 KiB
Makefile
75 lines
2.3 KiB
Makefile
all:
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include ../lib.mk
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.PHONY: all all_32 all_64 warn_32bit_failure clean
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TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall \
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check_initial_reg_state sigreturn ldt_gdt
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TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \
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test_FCMOV test_FCOMI test_FISTTP \
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vdso_restorer
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TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
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TARGETS_C_64BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_64BIT_ONLY)
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BINARIES_32 := $(TARGETS_C_32BIT_ALL:%=%_32)
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BINARIES_64 := $(TARGETS_C_64BIT_ALL:%=%_64)
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CFLAGS := -O2 -g -std=gnu99 -pthread -Wall
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UNAME_M := $(shell uname -m)
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CAN_BUILD_I386 := $(shell ./check_cc.sh $(CC) trivial_32bit_program.c -m32)
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CAN_BUILD_X86_64 := $(shell ./check_cc.sh $(CC) trivial_64bit_program.c)
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ifeq ($(CAN_BUILD_I386),1)
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all: all_32
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TEST_PROGS += $(BINARIES_32)
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endif
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ifeq ($(CAN_BUILD_X86_64),1)
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all: all_64
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TEST_PROGS += $(BINARIES_64)
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endif
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all_32: $(BINARIES_32)
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all_64: $(BINARIES_64)
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clean:
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$(RM) $(BINARIES_32) $(BINARIES_64)
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$(TARGETS_C_32BIT_ALL:%=%_32): %_32: %.c
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$(CC) -m32 -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl -lm
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$(TARGETS_C_64BIT_ALL:%=%_64): %_64: %.c
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$(CC) -m64 -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl
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# x86_64 users should be encouraged to install 32-bit libraries
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ifeq ($(CAN_BUILD_I386)$(CAN_BUILD_X86_64),01)
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all: warn_32bit_failure
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warn_32bit_failure:
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@echo "Warning: you seem to have a broken 32-bit build" 2>&1; \
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echo "environment. This will reduce test coverage of 64-bit" 2>&1; \
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echo "kernels. If you are using a Debian-like distribution," 2>&1; \
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echo "try:"; 2>&1; \
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echo ""; \
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echo " apt-get install gcc-multilib libc6-i386 libc6-dev-i386"; \
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echo ""; \
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echo "If you are using a Fedora-like distribution, try:"; \
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echo ""; \
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echo " yum install glibc-devel.*i686"; \
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exit 0;
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endif
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# Some tests have additional dependencies.
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sysret_ss_attrs_64: thunks.S
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ptrace_syscall_32: raw_syscall_helper_32.S
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test_syscall_vdso_32: thunks_32.S
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# check_initial_reg_state is special: it needs a custom entry, and it
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# needs to be static so that its interpreter doesn't destroy its initial
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# state.
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check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
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check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
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