From a37cd2a59d0cb270b1bba568fd3a3b8668b9d3ba Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Thu, 5 Oct 2023 11:06:36 +0200 Subject: x86/sev: Disable MMIO emulation from user mode A virt scenario can be constructed where MMIO memory can be user memory. When that happens, a race condition opens between when the hardware raises the #VC and when the #VC handler gets to emulate the instruction. If the MOVS is replaced with a MOVS accessing kernel memory in that small race window, then write to kernel memory happens as the access checks are not done at emulation time. Disable MMIO emulation in user mode temporarily until a sensible use case appears and justifies properly handling the race window. Fixes: 0118b604c2c9 ("x86/sev-es: Handle MMIO String Instructions") Reported-by: Tom Dohrmann Signed-off-by: Borislav Petkov (AMD) Tested-by: Tom Dohrmann Cc: --- arch/x86/kernel/sev.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch') diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 2787826d9f60..4ee14e647ae6 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -1509,6 +1509,9 @@ static enum es_result vc_handle_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt) return ES_DECODE_FAILED; } + if (user_mode(ctxt->regs)) + return ES_UNSUPPORTED; + switch (mmio) { case INSN_MMIO_WRITE: memcpy(ghcb->shared_buffer, reg_data, bytes); -- cgit From b9cb9c45583b911e0db71d09caa6b56469eb2bdf Mon Sep 17 00:00:00 2001 From: Joerg Roedel Date: Wed, 21 Jun 2023 17:42:42 +0200 Subject: x86/sev: Check IOBM for IOIO exceptions from user-space Check the IO permission bitmap (if present) before emulating IOIO #VC exceptions for user-space. These permissions are checked by hardware already before the #VC is raised, but due to the VC-handler decoding race it needs to be checked again in software. Fixes: 25189d08e516 ("x86/sev-es: Add support for handling IOIO exceptions") Reported-by: Tom Dohrmann Signed-off-by: Joerg Roedel Signed-off-by: Borislav Petkov (AMD) Tested-by: Tom Dohrmann Cc: --- arch/x86/boot/compressed/sev.c | 5 +++++ arch/x86/kernel/sev-shared.c | 22 +++++++++++++++------- arch/x86/kernel/sev.c | 27 +++++++++++++++++++++++++++ 3 files changed, 47 insertions(+), 7 deletions(-) (limited to 'arch') diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c index dc8c876fbd8f..afd91041ec3e 100644 --- a/arch/x86/boot/compressed/sev.c +++ b/arch/x86/boot/compressed/sev.c @@ -103,6 +103,11 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt, return ES_OK; } +static enum es_result vc_ioio_check(struct es_em_ctxt *ctxt, u16 port, size_t size) +{ + return ES_OK; +} + #undef __init #define __init diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c index 2eabccde94fb..bcd77c48be0a 100644 --- a/arch/x86/kernel/sev-shared.c +++ b/arch/x86/kernel/sev-shared.c @@ -656,6 +656,9 @@ static enum es_result vc_insn_string_write(struct es_em_ctxt *ctxt, static enum es_result vc_ioio_exitinfo(struct es_em_ctxt *ctxt, u64 *exitinfo) { struct insn *insn = &ctxt->insn; + size_t size; + u64 port; + *exitinfo = 0; switch (insn->opcode.bytes[0]) { @@ -664,7 +667,7 @@ static enum es_result vc_ioio_exitinfo(struct es_em_ctxt *ctxt, u64 *exitinfo) case 0x6d: *exitinfo |= IOIO_TYPE_INS; *exitinfo |= IOIO_SEG_ES; - *exitinfo |= (ctxt->regs->dx & 0xffff) << 16; + port = ctxt->regs->dx & 0xffff; break; /* OUTS opcodes */ @@ -672,41 +675,43 @@ static enum es_result vc_ioio_exitinfo(struct es_em_ctxt *ctxt, u64 *exitinfo) case 0x6f: *exitinfo |= IOIO_TYPE_OUTS; *exitinfo |= IOIO_SEG_DS; - *exitinfo |= (ctxt->regs->dx & 0xffff) << 16; + port = ctxt->regs->dx & 0xffff; break; /* IN immediate opcodes */ case 0xe4: case 0xe5: *exitinfo |= IOIO_TYPE_IN; - *exitinfo |= (u8)insn->immediate.value << 16; + port = (u8)insn->immediate.value & 0xffff; break; /* OUT immediate opcodes */ case 0xe6: case 0xe7: *exitinfo |= IOIO_TYPE_OUT; - *exitinfo |= (u8)insn->immediate.value << 16; + port = (u8)insn->immediate.value & 0xffff; break; /* IN register opcodes */ case 0xec: case 0xed: *exitinfo |= IOIO_TYPE_IN; - *exitinfo |= (ctxt->regs->dx & 0xffff) << 16; + port = ctxt->regs->dx & 0xffff; break; /* OUT register opcodes */ case 0xee: case 0xef: *exitinfo |= IOIO_TYPE_OUT; - *exitinfo |= (ctxt->regs->dx & 0xffff) << 16; + port = ctxt->regs->dx & 0xffff; break; default: return ES_DECODE_FAILED; } + *exitinfo |= port << 16; + switch (insn->opcode.bytes[0]) { case 0x6c: case 0x6e: @@ -716,12 +721,15 @@ static enum es_result vc_ioio_exitinfo(struct es_em_ctxt *ctxt, u64 *exitinfo) case 0xee: /* Single byte opcodes */ *exitinfo |= IOIO_DATA_8; + size = 1; break; default: /* Length determined by instruction parsing */ *exitinfo |= (insn->opnd_bytes == 2) ? IOIO_DATA_16 : IOIO_DATA_32; + size = (insn->opnd_bytes == 2) ? 2 : 4; } + switch (insn->addr_bytes) { case 2: *exitinfo |= IOIO_ADDR_16; @@ -737,7 +745,7 @@ static enum es_result vc_ioio_exitinfo(struct es_em_ctxt *ctxt, u64 *exitinfo) if (insn_has_rep_prefix(insn)) *exitinfo |= IOIO_REP; - return ES_OK; + return vc_ioio_check(ctxt, (u16)port, size); } static enum es_result vc_handle_ioio(struct ghcb *ghcb, struct es_em_ctxt *ctxt) diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 4ee14e647ae6..0f218932e844 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -524,6 +524,33 @@ static enum es_result vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt return ES_OK; } +static enum es_result vc_ioio_check(struct es_em_ctxt *ctxt, u16 port, size_t size) +{ + BUG_ON(size > 4); + + if (user_mode(ctxt->regs)) { + struct thread_struct *t = ¤t->thread; + struct io_bitmap *iobm = t->io_bitmap; + size_t idx; + + if (!iobm) + goto fault; + + for (idx = port; idx < port + size; ++idx) { + if (test_bit(idx, iobm->bitmap)) + goto fault; + } + } + + return ES_OK; + +fault: + ctxt->fi.vector = X86_TRAP_GP; + ctxt->fi.error_code = 0; + + return ES_EXCEPTION; +} + /* Include code shared with pre-decompression boot stage */ #include "sev-shared.c" -- cgit From 63e44bc52047f182601e7817da969a105aa1f721 Mon Sep 17 00:00:00 2001 From: Joerg Roedel Date: Mon, 16 Oct 2023 14:42:50 +0200 Subject: x86/sev: Check for user-space IOIO pointing to kernel space Check the memory operand of INS/OUTS before emulating the instruction. The #VC exception can get raised from user-space, but the memory operand can be manipulated to access kernel memory before the emulation actually begins and after the exception handler has run. [ bp: Massage commit message. ] Fixes: 597cfe48212a ("x86/boot/compressed/64: Setup a GHCB-based VC Exception handler") Reported-by: Tom Dohrmann Signed-off-by: Joerg Roedel Signed-off-by: Borislav Petkov (AMD) Cc: --- arch/x86/boot/compressed/sev.c | 5 +++++ arch/x86/kernel/sev-shared.c | 31 +++++++++++++++++++++++++++++-- 2 files changed, 34 insertions(+), 2 deletions(-) (limited to 'arch') diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c index afd91041ec3e..80d76aea1f7b 100644 --- a/arch/x86/boot/compressed/sev.c +++ b/arch/x86/boot/compressed/sev.c @@ -108,6 +108,11 @@ static enum es_result vc_ioio_check(struct es_em_ctxt *ctxt, u16 port, size_t si return ES_OK; } +static bool fault_in_kernel_space(unsigned long address) +{ + return false; +} + #undef __init #define __init diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c index bcd77c48be0a..4d729686f992 100644 --- a/arch/x86/kernel/sev-shared.c +++ b/arch/x86/kernel/sev-shared.c @@ -592,6 +592,23 @@ fail: sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ); } +static enum es_result vc_insn_string_check(struct es_em_ctxt *ctxt, + unsigned long address, + bool write) +{ + if (user_mode(ctxt->regs) && fault_in_kernel_space(address)) { + ctxt->fi.vector = X86_TRAP_PF; + ctxt->fi.error_code = X86_PF_USER; + ctxt->fi.cr2 = address; + if (write) + ctxt->fi.error_code |= X86_PF_WRITE; + + return ES_EXCEPTION; + } + + return ES_OK; +} + static enum es_result vc_insn_string_read(struct es_em_ctxt *ctxt, void *src, char *buf, unsigned int data_size, @@ -599,7 +616,12 @@ static enum es_result vc_insn_string_read(struct es_em_ctxt *ctxt, bool backwards) { int i, b = backwards ? -1 : 1; - enum es_result ret = ES_OK; + unsigned long address = (unsigned long)src; + enum es_result ret; + + ret = vc_insn_string_check(ctxt, address, false); + if (ret != ES_OK) + return ret; for (i = 0; i < count; i++) { void *s = src + (i * data_size * b); @@ -620,7 +642,12 @@ static enum es_result vc_insn_string_write(struct es_em_ctxt *ctxt, bool backwards) { int i, s = backwards ? -1 : 1; - enum es_result ret = ES_OK; + unsigned long address = (unsigned long)dst; + enum es_result ret; + + ret = vc_insn_string_check(ctxt, address, true); + if (ret != ES_OK) + return ret; for (i = 0; i < count; i++) { void *d = dst + (i * data_size * s); -- cgit