| Message ID | 20240712094630.29757-2-vigbalas@amd.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add XSAVE layout description to Core files for debuggers to support varying XSAVE layouts | expand |
On Fri, Jul 12 2024 at 15:16, Vignesh Balasubramanian wrote: > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h > index 1fb83d477..cad37090b 100644 > --- a/arch/x86/include/asm/elf.h > +++ b/arch/x86/include/asm/elf.h > @@ -13,6 +13,15 @@ > #include <asm/auxvec.h> > #include <asm/fsgsbase.h> > > +struct xfeat_component { > + u32 type; > + u32 size; > + u32 offset; > + u32 flags; > +} __packed; > + > +_Static_assert(sizeof(struct xfeat_component)%4 == 0, "xfeat_component is not aligned"); This struct is only used in xstate.c and asm/elf.h is not a UAPI header. So what's the point of declaring it in the header instead of xtsate.c? If this needs to provided for user space consumption, then it want's to be in a UAPI header, no? Thanks, tglx
On 7/13/2024 4:12 PM, Thomas Gleixner wrote: > Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding. > > > On Fri, Jul 12 2024 at 15:16, Vignesh Balasubramanian wrote: >> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h >> index 1fb83d477..cad37090b 100644 >> --- a/arch/x86/include/asm/elf.h >> +++ b/arch/x86/include/asm/elf.h >> @@ -13,6 +13,15 @@ >> #include <asm/auxvec.h> >> #include <asm/fsgsbase.h> >> >> +struct xfeat_component { >> + u32 type; >> + u32 size; >> + u32 offset; >> + u32 flags; >> +} __packed; >> + >> +_Static_assert(sizeof(struct xfeat_component)%4 == 0, "xfeat_component is not aligned"); > This struct is only used in xstate.c and asm/elf.h is not a UAPI > header. So what's the point of declaring it in the header instead of > xtsate.c? > > If this needs to provided for user space consumption, then it want's to > be in a UAPI header, no? Our initial idea is to pass the "struct xfeat_component" through "glibc". is "include/uapi/linux/elf.h" proper header to add this ? I couldn't see any proper header inside "arch/x86/include/uapi/asm/". Please advise. thanks, vigneshbalu > Thanks, > > tglx
On Wed, Jul 17, 2024 at 03:02:23PM +0530, Balasubrmanian, Vignesh wrote: > > On 7/13/2024 4:12 PM, Thomas Gleixner wrote: > > Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding. > > > > > > On Fri, Jul 12 2024 at 15:16, Vignesh Balasubramanian wrote: > > > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h > > > index 1fb83d477..cad37090b 100644 > > > --- a/arch/x86/include/asm/elf.h > > > +++ b/arch/x86/include/asm/elf.h > > > @@ -13,6 +13,15 @@ > > > #include <asm/auxvec.h> > > > #include <asm/fsgsbase.h> > > > > > > +struct xfeat_component { > > > + u32 type; > > > + u32 size; > > > + u32 offset; > > > + u32 flags; > > > +} __packed; > > > + > > > +_Static_assert(sizeof(struct xfeat_component)%4 == 0, "xfeat_component is not aligned"); > > This struct is only used in xstate.c and asm/elf.h is not a UAPI > > header. So what's the point of declaring it in the header instead of > > xtsate.c? > > > > If this needs to provided for user space consumption, then it want's to > > be in a UAPI header, no? > Our initial idea is to pass the "struct xfeat_component" through "glibc". > is "include/uapi/linux/elf.h" proper header to add this ? I'd rather not put arch-specific things in the main UAPI elf.h file unless there is a good reason. > I couldn't see any proper header inside "arch/x86/include/uapi/asm/". Other architectures have arch/*/include/uapi/asm/elf.h, so it may be time to add one for x86 too. For this to be UAPI, I would want to see more explicit namespacing, e.g. struct x86_xfeat_component, etc. -Kees
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 1d7122a18..0ea43da0b 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -107,6 +107,7 @@ config X86 select ARCH_HAS_DEBUG_WX select ARCH_HAS_ZONE_DMA_SET if EXPERT select ARCH_HAVE_NMI_SAFE_CMPXCHG + select ARCH_HAVE_EXTRA_ELF_NOTES select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI select ARCH_MIGHT_HAVE_PC_PARPORT diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 1fb83d477..cad37090b 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -13,6 +13,15 @@ #include <asm/auxvec.h> #include <asm/fsgsbase.h> +struct xfeat_component { + u32 type; + u32 size; + u32 offset; + u32 flags; +} __packed; + +_Static_assert(sizeof(struct xfeat_component)%4 == 0, "xfeat_component is not aligned"); + typedef unsigned long elf_greg_t; #define ELF_NGREG (sizeof(struct user_regs_struct) / sizeof(elf_greg_t)) diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index c5a026fee..5d59f390c 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -13,6 +13,7 @@ #include <linux/seq_file.h> #include <linux/proc_fs.h> #include <linux/vmalloc.h> +#include <linux/coredump.h> #include <asm/fpu/api.h> #include <asm/fpu/regset.h> @@ -1838,3 +1839,89 @@ int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns, return 0; } #endif /* CONFIG_PROC_PID_ARCH_STATUS */ + +#ifdef CONFIG_COREDUMP +static const char owner_name[] = "LINUX"; + +/* + * Dump type, size, offset and flag values for every xfeature that is present. + */ +static int dump_xsave_layout_desc(struct coredump_params *cprm) +{ + int num_records = 0; + int i; + + for_each_extended_xfeature(i, fpu_user_cfg.max_features) { + struct xfeat_component xc = { + .type = i, + .size = xstate_sizes[i], + .offset = xstate_offsets[i], + /* reserved for future use */ + .flags = 0, + }; + + if (!dump_emit(cprm, &xc, sizeof(xc))) + return 0; + + num_records++; + } + return num_records; +} + +static u32 get_xsave_desc_size(void) +{ + u32 cnt = 0; + u32 i; + + for_each_extended_xfeature(i, fpu_user_cfg.max_features) + cnt++; + + return cnt * (sizeof(struct xfeat_component)); +} + +int elf_coredump_extra_notes_write(struct coredump_params *cprm) +{ + int num_records = 0; + struct elf_note en; + + if (!fpu_user_cfg.max_features) + return 0; + + en.n_namesz = sizeof(owner_name); + en.n_descsz = get_xsave_desc_size(); + en.n_type = NT_X86_XSAVE_LAYOUT; + + if (!dump_emit(cprm, &en, sizeof(en))) + return 1; + if (!dump_emit(cprm, owner_name, en.n_namesz)) + return 1; + if (!dump_align(cprm, 4)) + return 1; + + num_records = dump_xsave_layout_desc(cprm); + if (!num_records) + return 1; + + /* Total size should be equal to the number of records */ + if ((sizeof(struct xfeat_component) * num_records) != en.n_descsz) + return 1; + + return 0; +} + +int elf_coredump_extra_notes_size(void) +{ + int size; + + if (!fpu_user_cfg.max_features) + return 0; + + /* .note header */ + size = sizeof(struct elf_note); + /* Name plus alignment to 4 bytes */ + size += roundup(sizeof(owner_name), 4); + size += get_xsave_desc_size(); + + return size; +} +#endif /* CONFIG_COREDUMP */ diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index a43897b03..3d15c7369 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -2006,7 +2006,7 @@ static int elf_core_dump(struct coredump_params *cprm) { size_t sz = info.size; - /* For cell spufs */ + /* For cell spufs and x86 xstate */ sz += elf_coredump_extra_notes_size(); phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL); @@ -2070,7 +2070,7 @@ static int elf_core_dump(struct coredump_params *cprm) if (!write_note_info(&info, cprm)) goto end_coredump; - /* For cell spufs */ + /* For cell spufs and x86 xstate */ if (elf_coredump_extra_notes_write(cprm)) goto end_coredump; diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h index b54b313bc..e30a9b47d 100644 --- a/include/uapi/linux/elf.h +++ b/include/uapi/linux/elf.h @@ -411,6 +411,7 @@ typedef struct elf64_shdr { #define NT_X86_XSTATE 0x202 /* x86 extended state using xsave */ /* Old binutils treats 0x203 as a CET state */ #define NT_X86_SHSTK 0x204 /* x86 SHSTK state */ +#define NT_X86_XSAVE_LAYOUT 0x205 /* XSAVE layout description */ #define NT_S390_HIGH_GPRS 0x300 /* s390 upper register halves */ #define NT_S390_TIMER 0x301 /* s390 timer register */ #define NT_S390_TODCMP 0x302 /* s390 TOD clock comparator register */
Add a new .note section containing type, size, offset and flags of every xfeature that is present. This information will be used by debuggers to understand the XSAVE layout of the machine where the core file has been dumped, and to read XSAVE registers, especially during cross-platform debugging. The XSAVE layouts of modern AMD and Intel CPUs differ, especially since Memory Protection Keys and the AVX-512 features have been inculcated into the AMD CPUs. Since AMD never adopted (and hence never left room in the XSAVE layout for) the Intel MPX feature. Tools like GDB had assumed a fixed XSAVE layout matching that of Intel (based on the XCR0 mask). Hence, core dumps from AMD CPUs didn't match the known size for the XCR0 mask. This resulted in GDB and other tools not being able to access the values of the AVX-512 and PKRU registers on AMD CPUs. To solve this, an interim solution has been accepted into GDB, and is already a part of GDB 14, see https://sourceware.org/pipermail/gdb-patches/2023-March/198081.html. But it depends on heuristics based on the total XSAVE register set size and the XCR0 mask to infer the layouts of the various register blocks for core dumps, and hence, is not a foolproof mechanism to determine the layout of the XSAVE area. Therefore, add a new core dump note in order to allow GDB/LLDB and other relevant tools to determine the layout of the XSAVE area of the machine where the corefile was dumped. The new core dump note (which is being proposed as a per-process .note section), NT_X86_XSAVE_LAYOUT (0x205) contains an array of structures. Each structure describes an individual extended feature containing offset, size and flags in this format: struct xfeat_component { u32 type; u32 size; u32 offset; u32 flags; }; and in an independent manner, allowing for future extensions without depending on hw arch specifics like CPUID etc. Co-developed-by: Jini Susan George <jinisusan.george@amd.com> Signed-off-by: Jini Susan George <jinisusan.george@amd.com> Co-developed-by: Borislav Petkov (AMD) <bp@alien8.de> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Signed-off-by: Vignesh Balasubramanian <vigbalas@amd.com> --- V2->v3: simplified code as per review comments. arch/x86/Kconfig | 1 + arch/x86/include/asm/elf.h | 9 ++++ arch/x86/kernel/fpu/xstate.c | 87 ++++++++++++++++++++++++++++++++++++ fs/binfmt_elf.c | 4 +- include/uapi/linux/elf.h | 1 + 5 files changed, 100 insertions(+), 2 deletions(-)