From: Pedro Alves Date: Tue, 26 Jun 2018 15:33:27 +0000 (+0100) Subject: x86_64-windows GDB crash due to fs_base/gs_base registers X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=de52b9607d2623f18b7a7dbee3e1123d8d63f5da;p=binutils-gdb.git x86_64-windows GDB crash due to fs_base/gs_base registers GDB is currently crashing anytime we try to access the fs_base/gs_base registers, either to read them, or to write them. This can be observed under various scenarios: - Explicit reference to those registers (eg: print $fs_base) -- probably relatively rare; - Calling a function in the inferior, with the crash happening because we are trying to read those registers in order to save their value ahead of making the function call; - Just a plain "info registers"; The crash was introduced by the following commit: | commit 48aeef91c248291dd03583798904612426b1f40a | Date: Mon Jun 26 18:14:43 2017 -0700 | Subject: Include the fs_base and gs_base registers in amd64 target descriptions. The Windows-nat implementation was unfortunately not prepared to deal with those new registers. In particular, the way it fetches registers is done by using a table where the index is the register number, and the value at that index is the offset in the area in the thread's CONTEXT data where the corresponding register value is stored. For instance, in amd64-windows-nat.c, we can find the mappings static array containing the following 57 elements in it: #define context_offset(x) (offsetof (CONTEXT, x)) static const int mappings[] = { context_offset (Rax), [...] context_offset (FloatSave.MxCsr) }; That array is then used by windows_fetch_one_register via: char *context_offset = ((char *) &th->context) + mappings[r]; The problem is that fs_base's register number is 172, which is well past the end of the mappings array (57 elements in total). We end up getting an undefined offset, which happens to be so large that it then causes the address where we try to read the register value (a little bit later) to be invalid, thus crashing GDB with a SEGV. This patch side-steps the issue entirely by removing support for those registers in GDB on x86_64-windows, because a look at the CONTEXT structure indicates no support for getting those registers. A more comprehensive fix would patch the potential buffer overflow of the mappings array, but this can be done as a separate commit. gdb/ChangeLog: * gdb/amd64-tdep.h (amd64_create_target_description): Add "segments" parameter. * gdb/amd64-tdep.c (amd64_none_init_abi, amd64_x32_none_init_abi) (_initialize_amd64_tdep): Update call to amd64_create_target_description. (amd64_target_description): Add "segments" parameter. Adjust the implementation to use it. * gdb/amd64-linux-tdep.c (amd64_linux_read_description): Update call to amd64_create_target_description. * gdb/amd64-windows-tdep.c (amd64_windows_init_abi): Likewise. * gdb/arch/amd64.h (amd64_create_target_description): Add "segments" register. * gdb/arch/amd64.c (amd64_create_target_description): Add "segments" parameter. Call create_feature_i386_64bit_segments only if SEGMENTS is true. * gdb/gdbserver/win32-i386-low.c (i386_arch_setup): Update call to amd64_create_target_description. Tested on x86_64-windows using AdaCore's testsuite (by Joel Brobecker ). --- diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 0cbccf5f8a6..c47c111466d 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,23 @@ +2018-06-29 Pedro Alves + + * gdb/amd64-tdep.h (amd64_create_target_description): Add + "segments" parameter. + * gdb/amd64-tdep.c (amd64_none_init_abi, amd64_x32_none_init_abi) + (_initialize_amd64_tdep): Update call to + amd64_create_target_description. + (amd64_target_description): Add "segments" parameter. Adjust + the implementation to use it. + * gdb/amd64-linux-tdep.c (amd64_linux_read_description): Update + call to amd64_create_target_description. + * gdb/amd64-windows-tdep.c (amd64_windows_init_abi): Likewise. + * gdb/arch/amd64.h (amd64_create_target_description): Add + "segments" register. + * gdb/arch/amd64.c (amd64_create_target_description): Add + "segments" parameter. Call create_feature_i386_64bit_segments + only if SEGMENTS is true. + * gdb/gdbserver/win32-i386-low.c (i386_arch_setup): Update + call to amd64_create_target_description. + 2018-06-29 Pedro Alves * thread.c (thread_target_id_str): New, factored out from ... diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c index ef9248d708d..7fe37d83f69 100644 --- a/gdb/amd64-linux-tdep.c +++ b/gdb/amd64-linux-tdep.c @@ -1594,7 +1594,8 @@ amd64_linux_read_description (uint64_t xcr0_features_bit, bool is_x32) } if (*tdesc == NULL) - *tdesc = amd64_create_target_description (xcr0_features_bit, is_x32, true); + *tdesc = amd64_create_target_description (xcr0_features_bit, is_x32, + true, true); return *tdesc; } diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c index 9f8f018dd15..190e086ebfe 100644 --- a/gdb/amd64-tdep.c +++ b/gdb/amd64-tdep.c @@ -3225,7 +3225,8 @@ amd64_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch, static void amd64_none_init_abi (gdbarch_info info, gdbarch *arch) { - amd64_init_abi (info, arch, amd64_target_description (X86_XSTATE_SSE_MASK)); + amd64_init_abi (info, arch, amd64_target_description (X86_XSTATE_SSE_MASK, + true)); } static struct type * @@ -3266,25 +3267,27 @@ static void amd64_x32_none_init_abi (gdbarch_info info, gdbarch *arch) { amd64_x32_init_abi (info, arch, - amd64_target_description (X86_XSTATE_SSE_MASK)); + amd64_target_description (X86_XSTATE_SSE_MASK, true)); } /* Return the target description for a specified XSAVE feature mask. */ const struct target_desc * -amd64_target_description (uint64_t xcr0) +amd64_target_description (uint64_t xcr0, bool segments) { static target_desc *amd64_tdescs \ - [2/*AVX*/][2/*MPX*/][2/*AVX512*/][2/*PKRU*/] = {}; + [2/*AVX*/][2/*MPX*/][2/*AVX512*/][2/*PKRU*/][2/*segments*/] = {}; target_desc **tdesc; tdesc = &amd64_tdescs[(xcr0 & X86_XSTATE_AVX) ? 1 : 0] [(xcr0 & X86_XSTATE_MPX) ? 1 : 0] [(xcr0 & X86_XSTATE_AVX512) ? 1 : 0] - [(xcr0 & X86_XSTATE_PKRU) ? 1 : 0]; + [(xcr0 & X86_XSTATE_PKRU) ? 1 : 0] + [segments ? 1 : 0]; if (*tdesc == NULL) - *tdesc = amd64_create_target_description (xcr0, false, false); + *tdesc = amd64_create_target_description (xcr0, false, false, + segments); return *tdesc; } @@ -3314,7 +3317,7 @@ _initialize_amd64_tdep (void) for (auto &a : xml_masks) { - auto tdesc = amd64_target_description (a.mask); + auto tdesc = amd64_target_description (a.mask, true); selftests::record_xml_tdesc (a.xml, tdesc); } diff --git a/gdb/amd64-tdep.h b/gdb/amd64-tdep.h index 7d3791ad936..94e012632ff 100644 --- a/gdb/amd64-tdep.h +++ b/gdb/amd64-tdep.h @@ -106,7 +106,8 @@ extern void amd64_init_abi (struct gdbarch_info info, extern void amd64_x32_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch, const target_desc *default_tdesc); -extern const struct target_desc *amd64_target_description (uint64_t xcr0); +extern const struct target_desc *amd64_target_description (uint64_t xcr0, + bool segments); /* Fill register REGNUM in REGCACHE with the appropriate floating-point or SSE register value from *FXSAVE. If REGNUM is diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c index 83a7f2f32ed..904875baccd 100644 --- a/gdb/amd64-windows-tdep.c +++ b/gdb/amd64-windows-tdep.c @@ -1226,7 +1226,7 @@ amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch) frame_unwind_append_unwinder (gdbarch, &amd64_windows_frame_unwind); amd64_init_abi (info, gdbarch, - amd64_target_description (X86_XSTATE_SSE_MASK)); + amd64_target_description (X86_XSTATE_SSE_MASK, false)); windows_init_abi (info, gdbarch); diff --git a/gdb/arch/amd64.c b/gdb/arch/amd64.c index d31d8f1f75a..4ad17c3fdcd 100644 --- a/gdb/arch/amd64.c +++ b/gdb/arch/amd64.c @@ -33,10 +33,12 @@ /* Create amd64 target descriptions according to XCR0. If IS_X32 is true, create the x32 ones. If IS_LINUX is true, create target - descriptions for Linux. */ + descriptions for Linux. If SEGMENTS is true, then include + the "org.gnu.gdb.i386.segments" feature registers. */ target_desc * -amd64_create_target_description (uint64_t xcr0, bool is_x32, bool is_linux) +amd64_create_target_description (uint64_t xcr0, bool is_x32, bool is_linux, + bool segments) { target_desc *tdesc = allocate_target_description (); @@ -57,7 +59,8 @@ amd64_create_target_description (uint64_t xcr0, bool is_x32, bool is_linux) regnum = create_feature_i386_64bit_sse (tdesc, regnum); if (is_linux) regnum = create_feature_i386_64bit_linux (tdesc, regnum); - regnum = create_feature_i386_64bit_segments (tdesc, regnum); + if (segments) + regnum = create_feature_i386_64bit_segments (tdesc, regnum); if (xcr0 & X86_XSTATE_AVX) regnum = create_feature_i386_64bit_avx (tdesc, regnum); diff --git a/gdb/arch/amd64.h b/gdb/arch/amd64.h index c0c4dc27efe..4a659657da1 100644 --- a/gdb/arch/amd64.h +++ b/gdb/arch/amd64.h @@ -19,4 +19,4 @@ #include target_desc *amd64_create_target_description (uint64_t xcr0, bool is_x32, - bool is_linux); + bool is_linux, bool segments); diff --git a/gdb/gdbserver/win32-i386-low.c b/gdb/gdbserver/win32-i386-low.c index 16fe2c85b2a..62221688cbd 100644 --- a/gdb/gdbserver/win32-i386-low.c +++ b/gdb/gdbserver/win32-i386-low.c @@ -436,7 +436,7 @@ i386_arch_setup (void) #ifdef __x86_64__ tdesc = amd64_create_target_description (X86_XSTATE_SSE_MASK, false, - false); + false, false); const char **expedite_regs = amd64_expedite_regs; #else tdesc = i386_create_target_description (X86_XSTATE_SSE_MASK, false);