From b74a5ea8399d1a0466c55332f557863acdae21b6 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Tue, 24 Sep 2024 14:34:30 +0200 Subject: [PATCH 20/35] x86/pv: Fix merging of new status bits into %dr6 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit All #DB exceptions result in an update of %dr6, but this isn't captured in Xen's handling, and is buggy just about everywhere. To begin resolving this issue, add a new pending_dbg field to x86_event (unioned with cr2 to avoid taking any extra space, adjusting users to avoid old-GCC bugs with anonymous unions), and introduce pv_inject_DB() to replace the current callers using pv_inject_hw_exception(). Push the adjustment of v->arch.dr6 into pv_inject_event(), and use the new x86_merge_dr6() rather than the current incorrect logic. A key property is that pending_dbg is taken with positive polarity to deal with RTM/BLD sensibly. Most callers pass in a constant, but callers passing in a hardware %dr6 value need to XOR the value with X86_DR6_DEFAULT to flip to positive polarity. This fixes the behaviour of the breakpoint status bits; that any left pending are generally discarded when a new #DB is raised. In principle it would fix RTM/BLD too, except PV guests can't turn these capabilities on to start with. Signed-off-by: Andrew Cooper Reviewed-by: Roger Pau Monné Reviewed-by: Jan Beulich master commit: db39fa4b27ea470902d4625567cb6fa24030ddfa master date: 2024-08-21 23:59:19 +0100 --- xen/arch/x86/include/asm/domain.h | 18 ++++++++++++++++-- xen/arch/x86/include/asm/hvm/hvm.h | 3 ++- xen/arch/x86/pv/emul-priv-op.c | 5 +---- xen/arch/x86/pv/emulate.c | 9 +++++++-- xen/arch/x86/pv/ro-page-fault.c | 2 +- xen/arch/x86/pv/traps.c | 16 ++++++++++++---- xen/arch/x86/traps.c | 2 +- xen/arch/x86/x86_emulate/x86_emulate.h | 5 ++++- 8 files changed, 44 insertions(+), 16 deletions(-) diff --git a/xen/arch/x86/include/asm/domain.h b/xen/arch/x86/include/asm/domain.h index f5daeb182b..5d92891e6f 100644 --- a/xen/arch/x86/include/asm/domain.h +++ b/xen/arch/x86/include/asm/domain.h @@ -731,15 +731,29 @@ static inline void pv_inject_hw_exception(unsigned int vector, int errcode) pv_inject_event(&event); } +static inline void pv_inject_DB(unsigned long pending_dbg) +{ + struct x86_event event = { + .vector = X86_EXC_DB, + .type = X86_EVENTTYPE_HW_EXCEPTION, + .error_code = X86_EVENT_NO_EC, + }; + + event.pending_dbg = pending_dbg; + + pv_inject_event(&event); +} + static inline void pv_inject_page_fault(int errcode, unsigned long cr2) { - const struct x86_event event = { + struct x86_event event = { .vector = X86_EXC_PF, .type = X86_EVENTTYPE_HW_EXCEPTION, .error_code = errcode, - .cr2 = cr2, }; + event.cr2 = cr2; + pv_inject_event(&event); } diff --git a/xen/arch/x86/include/asm/hvm/hvm.h b/xen/arch/x86/include/asm/hvm/hvm.h index 1c01e22c8e..238eece0cf 100644 --- a/xen/arch/x86/include/asm/hvm/hvm.h +++ b/xen/arch/x86/include/asm/hvm/hvm.h @@ -525,9 +525,10 @@ static inline void hvm_inject_page_fault(int errcode, unsigned long cr2) .vector = X86_EXC_PF, .type = X86_EVENTTYPE_HW_EXCEPTION, .error_code = errcode, - .cr2 = cr2, }; + event.cr2 = cr2; + hvm_inject_event(&event); } diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c index aa11ecadaa..15c83b9d23 100644 --- a/xen/arch/x86/pv/emul-priv-op.c +++ b/xen/arch/x86/pv/emul-priv-op.c @@ -1366,10 +1366,7 @@ int pv_emulate_privileged_op(struct cpu_user_regs *regs) ctxt.bpmatch |= DR_STEP; if ( ctxt.bpmatch ) - { - curr->arch.dr6 |= ctxt.bpmatch | DR_STATUS_RESERVED_ONE; - pv_inject_hw_exception(X86_EXC_DB, X86_EVENT_NO_EC); - } + pv_inject_DB(ctxt.bpmatch); /* fall through */ case X86EMUL_RETRY: diff --git a/xen/arch/x86/pv/emulate.c b/xen/arch/x86/pv/emulate.c index e7a1c0a2cc..8c44dea123 100644 --- a/xen/arch/x86/pv/emulate.c +++ b/xen/arch/x86/pv/emulate.c @@ -71,10 +71,15 @@ void pv_emul_instruction_done(struct cpu_user_regs *regs, unsigned long rip) { regs->rip = rip; regs->eflags &= ~X86_EFLAGS_RF; + if ( regs->eflags & X86_EFLAGS_TF ) { - current->arch.dr6 |= DR_STEP | DR_STATUS_RESERVED_ONE; - pv_inject_hw_exception(X86_EXC_DB, X86_EVENT_NO_EC); + /* + * TODO: this should generally use TF from the start of the + * instruction. It's only a latent bug for now, as this path isn't + * used for any instruction which modifies eflags. + */ + pv_inject_DB(X86_DR6_BS); } } diff --git a/xen/arch/x86/pv/ro-page-fault.c b/xen/arch/x86/pv/ro-page-fault.c index cad28ef928..d0fe07e3a1 100644 --- a/xen/arch/x86/pv/ro-page-fault.c +++ b/xen/arch/x86/pv/ro-page-fault.c @@ -390,7 +390,7 @@ int pv_ro_page_fault(unsigned long addr, struct cpu_user_regs *regs) /* Fallthrough */ case X86EMUL_OKAY: if ( ctxt.retire.singlestep ) - pv_inject_hw_exception(X86_EXC_DB, X86_EVENT_NO_EC); + pv_inject_DB(X86_DR6_BS); /* Fallthrough */ case X86EMUL_RETRY: diff --git a/xen/arch/x86/pv/traps.c b/xen/arch/x86/pv/traps.c index 83e84e2762..5a7341abf0 100644 --- a/xen/arch/x86/pv/traps.c +++ b/xen/arch/x86/pv/traps.c @@ -12,6 +12,7 @@ #include #include +#include #include #include #include @@ -50,9 +51,9 @@ void pv_inject_event(const struct x86_event *event) tb->cs = ti->cs; tb->eip = ti->address; - if ( event->type == X86_EVENTTYPE_HW_EXCEPTION && - vector == X86_EXC_PF ) + switch ( vector | -(event->type == X86_EVENTTYPE_SW_INTERRUPT) ) { + case X86_EXC_PF: curr->arch.pv.ctrlreg[2] = event->cr2; arch_set_cr2(curr, event->cr2); @@ -62,9 +63,16 @@ void pv_inject_event(const struct x86_event *event) error_code |= PFEC_user_mode; trace_pv_page_fault(event->cr2, error_code); - } - else + break; + + case X86_EXC_DB: + curr->arch.dr6 = x86_merge_dr6(curr->domain->arch.cpu_policy, + curr->arch.dr6, event->pending_dbg); + fallthrough; + default: trace_pv_trap(vector, regs->rip, use_error_code, error_code); + break; + } if ( use_error_code ) { diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index 78e83f6fc1..8e2df3e719 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -2032,7 +2032,7 @@ void asmlinkage do_debug(struct cpu_user_regs *regs) return; } - pv_inject_hw_exception(X86_EXC_DB, X86_EVENT_NO_EC); + pv_inject_DB(0 /* N/A, already merged */); } void asmlinkage do_entry_CP(struct cpu_user_regs *regs) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h b/xen/arch/x86/x86_emulate/x86_emulate.h index d92be69d84..e8a0e57228 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.h +++ b/xen/arch/x86/x86_emulate/x86_emulate.h @@ -78,7 +78,10 @@ struct x86_event { uint8_t type; /* X86_EVENTTYPE_* */ uint8_t insn_len; /* Instruction length */ int32_t error_code; /* X86_EVENT_NO_EC if n/a */ - unsigned long cr2; /* Only for X86_EXC_PF h/w exception */ + union { + unsigned long cr2; /* #PF */ + unsigned long pending_dbg; /* #DB (new DR6 bits, positive polarity) */ + }; }; /* -- 2.46.1