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x86/entry/xen: Route #DB correctly on Xen PV

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On Xen PV, #DB doesn't use IST. It still needs to be correctly routed
depending on whether it came from user or kernel mode.

Get rid of DECLARE/DEFINE_IDTENTRY_XEN -- it was too hard to follow the
logic.  Instead, route #DB and NMI through DECLARE/DEFINE_IDTENTRY_RAW on
Xen, and do the right thing for #DB.  Also add more warnings to the
exc_debug* handlers to make this type of failure more obvious.

This fixes various forms of corruption that happen when usermode
triggers #DB on Xen PV.

Fixes: 4c0dcd8350 ("x86/entry: Implement user mode C entry points for #DB and #MCE")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/4163e733cce0b41658e252c6c6b3464f33fdff17.1593795633.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski
2020-07-03 10:02:55 -07:00
committed by Thomas Gleixner
parent 3c73b81a91
commit f41f082422
4 changed files with 44 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

28
arch/x86/xen/enlighten_pv.c
View File

@@ -598,6 +598,26 @@ static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
}
#ifdef CONFIG_X86_64
void noist_exc_debug(struct pt_regs *regs);
DEFINE_IDTENTRY_RAW(xenpv_exc_nmi)
{
/* On Xen PV, NMI doesn't use IST. The C part is the sane as native. */
exc_nmi(regs);
}
DEFINE_IDTENTRY_RAW(xenpv_exc_debug)
{
/*
* There's no IST on Xen PV, but we still need to dispatch
* to the correct handler.
*/
if (user_mode(regs))
noist_exc_debug(regs);
else
exc_debug(regs);
}
struct trap_array_entry {
void (*orig)(void);
void (*xen)(void);
@@ -609,18 +629,18 @@ struct trap_array_entry {
.xen = xen_asm_##func, \
.ist_okay = ist_ok }
#define TRAP_ENTRY_REDIR(func, xenfunc, ist_ok) { \
#define TRAP_ENTRY_REDIR(func, ist_ok) { \
.orig = asm_##func, \
.xen = xen_asm_##xenfunc, \
.xen = xen_asm_xenpv_##func, \
.ist_okay = ist_ok }
static struct trap_array_entry trap_array[] = {
TRAP_ENTRY_REDIR(exc_debug, exc_xendebug, true ),
TRAP_ENTRY_REDIR(exc_debug, true ),
TRAP_ENTRY(exc_double_fault, true ),
#ifdef CONFIG_X86_MCE
TRAP_ENTRY(exc_machine_check, true ),
#endif
TRAP_ENTRY_REDIR(exc_nmi, exc_xennmi, true ),
TRAP_ENTRY_REDIR(exc_nmi, true ),
TRAP_ENTRY(exc_int3, false ),
TRAP_ENTRY(exc_overflow, false ),
#ifdef CONFIG_IA32_EMULATION

5
arch/x86/xen/xen-asm_64.S
View File

@@ -29,10 +29,9 @@ _ASM_NOKPROBE(xen_\name)
.endm
xen_pv_trap asm_exc_divide_error
xen_pv_trap asm_exc_debug
xen_pv_trap asm_exc_xendebug
xen_pv_trap asm_xenpv_exc_debug
xen_pv_trap asm_exc_int3
xen_pv_trap asm_exc_xennmi
xen_pv_trap asm_xenpv_exc_nmi
xen_pv_trap asm_exc_overflow
xen_pv_trap asm_exc_bounds
xen_pv_trap asm_exc_invalid_op