From: David Woodhouse <d...@amazon.co.uk> In e820_add_entry() the e820_table is reallocated with g_renew() to make space for a new entry. However, fw_cfg_arch_create() just uses the existing e820_table pointer.
This leads to a use-after-free if anything adds a new entry after fw_cfg is set up. Shift the addition of the etc/e820 file to the machine done notifier, and add a sanity check to ensure that e820_table isn't modified after the pointer gets stashed. Signed-off-by: David Woodhouse <d...@amazon.co.uk> --- hw/i386/e820_memory_layout.c | 8 ++++++++ hw/i386/fw_cfg.c | 7 ++++--- hw/i386/microvm.c | 5 +++-- 3 files changed, 15 insertions(+), 5 deletions(-) diff --git a/hw/i386/e820_memory_layout.c b/hw/i386/e820_memory_layout.c index 06970ac44a..c96515909e 100644 --- a/hw/i386/e820_memory_layout.c +++ b/hw/i386/e820_memory_layout.c @@ -8,13 +8,20 @@ #include "qemu/osdep.h" #include "qemu/bswap.h" +#include "qemu/error-report.h" #include "e820_memory_layout.h" static size_t e820_entries; struct e820_entry *e820_table; +static gboolean e820_done; int e820_add_entry(uint64_t address, uint64_t length, uint32_t type) { + if (e820_done) { + warn_report("warning: E820 modified after being consumed"); + return -1; + } + /* new "etc/e820" file -- include ram and reserved entries */ e820_table = g_renew(struct e820_entry, e820_table, e820_entries + 1); e820_table[e820_entries].address = cpu_to_le64(address); @@ -27,6 +34,7 @@ int e820_add_entry(uint64_t address, uint64_t length, uint32_t type) int e820_get_num_entries(void) { + e820_done = true; return e820_entries; } diff --git a/hw/i386/fw_cfg.c b/hw/i386/fw_cfg.c index 6e0d9945d0..e046ad1a54 100644 --- a/hw/i386/fw_cfg.c +++ b/hw/i386/fw_cfg.c @@ -102,6 +102,10 @@ void fw_cfg_build_smbios(PCMachineState *pcms, FWCfgState *fw_cfg, smbios_anchor, smbios_anchor_len); } #endif + + /* Add etc/e820 late, once all regions should be present */ + fw_cfg_add_file(fw_cfg, "etc/e820", e820_table, + sizeof(struct e820_entry) * e820_get_num_entries()); } FWCfgState *fw_cfg_arch_create(MachineState *ms, @@ -139,9 +143,6 @@ FWCfgState *fw_cfg_arch_create(MachineState *ms, #endif fw_cfg_add_i32(fw_cfg, FW_CFG_IRQ0_OVERRIDE, 1); - fw_cfg_add_file(fw_cfg, "etc/e820", e820_table, - sizeof(struct e820_entry) * e820_get_num_entries()); - fw_cfg_add_bytes(fw_cfg, FW_CFG_HPET, &hpet_cfg, sizeof(hpet_cfg)); /* allocate memory for the NUMA channel: one (64bit) word for the number * of nodes, one word for each VCPU->node and one word for each node to diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c index fec63cacfa..89b2abcebf 100644 --- a/hw/i386/microvm.c +++ b/hw/i386/microvm.c @@ -324,8 +324,6 @@ static void microvm_memory_init(MicrovmMachineState *mms) fw_cfg_add_i16(fw_cfg, FW_CFG_MAX_CPUS, machine->smp.max_cpus); fw_cfg_add_i64(fw_cfg, FW_CFG_RAM_SIZE, (uint64_t)machine->ram_size); fw_cfg_add_i32(fw_cfg, FW_CFG_IRQ0_OVERRIDE, 1); - fw_cfg_add_file(fw_cfg, "etc/e820", e820_table, - sizeof(struct e820_entry) * e820_get_num_entries()); rom_set_fw(fw_cfg); @@ -586,9 +584,12 @@ static void microvm_machine_done(Notifier *notifier, void *data) { MicrovmMachineState *mms = container_of(notifier, MicrovmMachineState, machine_done); + X86MachineState *x86ms = X86_MACHINE(mms); acpi_setup_microvm(mms); dt_setup_microvm(mms); + fw_cfg_add_file(x86ms->fw_cfg, "etc/e820", e820_table, + sizeof(struct e820_entry) * e820_get_num_entries()); } static void microvm_powerdown_req(Notifier *notifier, void *data) -- 2.44.0
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