From a47e3c26b1a07292e18658e9d33425f61b4716d1 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Tue, 7 Jul 2026 11:41:35 +0100 Subject: [PATCH 1/2] linux-user: Validate guest-passed dm_ioctl data_size In do_ioctl_dm() we work with a struct dm_ioctl from the guest. This has a fixed initial part, and then a variable data part; the guest tells us how long that part is by setting the data_size field. The data_size is supposed to include the length of the fixed parts of the struct dm_ioctl. Currently we don't validate anything about the guest-provided data_size, and we use it to allocate a buffer which we then copy the fixed part of the dm_ioctl struct into. This means that if the guest passes a very small data_size the copy of the fixed part will overrun the buffer. Perform the same sanitizing of the minimum and maximum limits of the data_size that the kernel does in drivers/md/dm-ioctl.c in the copy_params() function. Cc: qemu-stable@nongnu.org Fixes: 56e904ecb2018 ("linux-user: implement device mapper ioctls") Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3736 Signed-off-by: Peter Maydell Reviewed-by: Helge Deller Signed-off-by: Helge Deller --- linux-user/syscall.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index d257fb9ca9..3f060ee8b6 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -5088,6 +5088,9 @@ do_ioctl_usbdevfs_submiturb(const IOCTLEntry *ie, uint8_t *buf_temp, } #endif /* CONFIG_USBFS */ +#define DM_MAX_TARGETS 1048576 +#define DM_MAX_TARGET_PARAMS 1024 + static abi_long do_ioctl_dm(const IOCTLEntry *ie, uint8_t *buf_temp, int fd, int cmd, abi_long arg) { @@ -5100,6 +5103,7 @@ static abi_long do_ioctl_dm(const IOCTLEntry *ie, uint8_t *buf_temp, int fd, abi_long ret; void *big_buf = NULL; char *host_data; + const size_t minimum_data_size = offsetof(struct dm_ioctl, data); arg_type++; target_size = thunk_type_size(arg_type, 0); @@ -5111,9 +5115,26 @@ static abi_long do_ioctl_dm(const IOCTLEntry *ie, uint8_t *buf_temp, int fd, thunk_convert(buf_temp, argptr, arg_type, THUNK_HOST); unlock_user(argptr, arg, 0); - /* buf_temp is too small, so fetch things into a bigger buffer */ - big_buf = g_malloc0(((struct dm_ioctl*)buf_temp)->data_size * 2); - memcpy(big_buf, buf_temp, target_size); + /* At this point this includes the size of the fixed dm_ioctl parts */ + guest_data_size = ((struct dm_ioctl *)buf_temp)->data_size; + + if (guest_data_size < minimum_data_size || + guest_data_size > DM_MAX_TARGETS * DM_MAX_TARGET_PARAMS) { + ret = -TARGET_EINVAL; + goto out; + } + + /* + * buf_temp is too small, so fetch things into a bigger buffer. Here + * we copy all of the fixed parts of struct dm_ioctl but not the + * data at the end (which in the struct is "char data[7]" but in + * reality is command-specific and might be nothing or might be + * much larger, as defined by data_size). We know struct dm_ioctl's + * size is not target specific so we don't need to distinguish between + * its minimum size for the host vs the target. + */ + big_buf = g_malloc0(guest_data_size * 2); + memcpy(big_buf, buf_temp, minimum_data_size); buf_temp = big_buf; host_dm = big_buf; @@ -5122,7 +5143,8 @@ static abi_long do_ioctl_dm(const IOCTLEntry *ie, uint8_t *buf_temp, int fd, ret = -TARGET_EINVAL; goto out; } - guest_data_size = host_dm->data_size - host_dm->data_start; + /* Adjust down to only the size of the payload */ + guest_data_size -= host_dm->data_start; host_data = (char*)host_dm + host_dm->data_start; argptr = lock_user(VERIFY_READ, guest_data, guest_data_size, 1); From 7a2e863f9dd52883d6f59bb425f30609fc14aee4 Mon Sep 17 00:00:00 2001 From: Matt Turner Date: Sun, 12 Jul 2026 21:36:07 -0400 Subject: [PATCH 2/2] linux-user/alpha: populate AT_HWCAP from env->amask Alpha has never set AT_HWCAP in linux-user emulation, so getauxval(AT_HWCAP) always returned 0 regardless of the emulated CPU model. The Linux kernel computes ELF_HWCAP as ~amask(-1), i.e. the set of ISA extension bits that the amask instruction reports as supported (cleared in its output). env->amask stores exactly those bits with the same layout (BWX=0x1, FIX=0x2, CIX=0x4, MVI=0x100, TRAP=0x200, PREFETCH=0x1000), so returning it directly from get_elf_hwcap matches the kernel convention. Add HAVE_ELF_HWCAP to target_elf.h and implement get_elf_hwcap() in elfload.c to expose the emulated CPU's capability mask to user-space programs via the auxiliary vector. Without this fix, programs using getauxval(AT_HWCAP) to detect BWX/FIX/CIX (such as glibc's memcpy or JIT compilers targeting Alpha) incorrectly concluded that no extensions were available even when emulating ev56+. Signed-off-by: Matt Turner Cc: qemu-stable@nongnu.org Reviewed-by: Helge Deller Signed-off-by: Helge Deller --- linux-user/alpha/elfload.c | 11 +++++++++++ linux-user/alpha/target_elf.h | 1 + 2 files changed, 12 insertions(+) diff --git a/linux-user/alpha/elfload.c b/linux-user/alpha/elfload.c index 1969f620a5..7be9e466b6 100644 --- a/linux-user/alpha/elfload.c +++ b/linux-user/alpha/elfload.c @@ -6,6 +6,17 @@ #include "target_elf.h" +abi_ulong get_elf_hwcap(CPUState *cs) +{ + /* + * The Linux kernel computes ELF_HWCAP as ~amask(-1), which clears a bit + * for each supported ISA extension. env->amask stores exactly those bits + * set for the extensions supported by the emulated CPU model, matching + * the kernel's convention: bit set in AT_HWCAP ↔ extension present. + */ + return cpu_env(cs)->amask; +} + void elf_core_copy_regs(target_elf_gregset_t *r, const CPUAlphaState *env) { int i; diff --git a/linux-user/alpha/target_elf.h b/linux-user/alpha/target_elf.h index 4987ae3944..dd90c6f783 100644 --- a/linux-user/alpha/target_elf.h +++ b/linux-user/alpha/target_elf.h @@ -12,6 +12,7 @@ #define ELF_MACHINE EM_ALPHA #define HAVE_ELF_CORE_DUMP 1 +#define HAVE_ELF_HWCAP 1 /* * Matches the kernel's elf_gregset_t (ELF_NGREG = 33):